Two-year dermal carcinogenicity bioassay of triclosan in B6C3F1 mice

Triclosan is a widely used antimicrobial agent in personal care products, household items, medical devices, and clinical settings. Due to its extensive use, there is potential for humans in all age groups to receive lifetime exposures to triclosan, yet data on the chronic dermal toxicity/carcinogenicity of triclosan are still lacking. We evaluated the toxicity/carcinogenicity of triclosan administered dermally to B6C3F1 mice for 104 weeks. Groups of 48 male and 48 female B6C3F1 mice received dermal applications of 0, 1.25, 2.7, 5.8, or 12.5 mg triclosan/kg body weight (bw)/day in 95% ethanol, 7 days/week for 104 weeks. Vehicle control animals received 95% ethanol only; untreated, naïve control mice did not receive any treatment. There were no significant differences in survival among the groups. The highest dose of triclosan significantly decreased the body weight of mice in both sexes, but the decrease was ≤ 9%. Minimal-to-mild epidermal hyperplasia, suppurative inflammation (males only), and ulceration (males only) were observed at the application site in the treated groups, with the highest incidence occurring in the 12.5 mg triclosan/kg bw/day group. No tumors were identified at the application site. Female mice had a positive trend in the incidence of pancreatic islet adenoma. In male mice, there were positive trends in the incidences of hepatocellular carcinoma and hepatocellular adenoma or carcinoma (combined), with the increase of carcinoma being significant in the 5.8 and 12.5 mg/kg/day groups and the increase in hepatocellular adenoma or carcinoma (combined) being significant in the 2.7, 5.8, and 12.5 mg/kg/day groups.

Toxicological evaluation of brominated vegetable oil in Sprague Dawley rats

Brominated vegetable oil (BVO) has been approved by the US Food and Drug Administration on an interim basis as a food additive. Past studies have raised concerns about potential toxicities from consuming BVO. To investigate further these toxicities, we conducted a 90-day dietary exposure study in Sprague Dawley rats and analyzed tissue distribution of the main metabolites. Six-week-old male and female rats were fed diets containing 0 (control), 0.002%, 0.02%, 0.1%, or 0.5% BVO by weight. Statistically significant increases were observed in the serum bromide in the high-dose group of both sexes and in the incidence of thyroid follicular cell hypertrophy in the two highest dose groups of males and the high-dose group of females. An increase in serum TSH was observed in the high-dose group for both sexes, as well as a decrease in serum T4 in the high-dose males. A clear dose-response was observed in di- and tetra-bromostearic acid levels in the heart, liver, and inguinal fat. These data expand upon previous observations in rats and pigs that oral exposure to BVO is associated with increased tissue levels of inorganic and organic bromine, and that the thyroid is a potential target organ of toxicity.

Effect of urinary pH upon the renal toxicity of melamine and cyanuric acid

In 2007, dietary exposure to "scrap melamine' resulted in the death of a large number of cats and dogs, which was attributed to the formation of melamine cyanurate crystals in their kidneys. In this study, we investigated if changes in urinary pH could diminish the renal toxicity associated with exposure to combinations of melamine and cyanuric acid. Female Sprague-Dawley rats were treated for three days with suspensions of melamine and cyanuric acid at doses that were expected to induce renal toxicity. Dosing was then discontinued and the rats were treated for seven days with drinking water solutions (i.e., ammonium chloride and sodium bicarbonate) that would alter urinary pH. The urinary pH of rats administered ammonium chloride drinking water decreased from pH 6.0-6.2 to pH 5.1-5.2. This was accompanied by a decrease in the incidence of melamine cyanurate crystals in the kidneys and a decrease in the incidence of renal lesions. These data suggest that acidification of urine may help overcome the renal toxicities associated with the formation of melamine cyanurate crystals in the kidney.

Characterization of the variability in the extent of nonalcoholic fatty liver induced by a high-fat diet in the genetically diverse Collaborative Cross mouse model

Interindividual variability and sexual dimorphisms in the development of nonalcoholic fatty liver disease (NAFLD) are still poorly understood. In the present study, male and female strains of Collaborative Cross (CC) mice were fed a high-fat and high-sucrose (HF/HS) diet or a control diet for 12 weeks to investigate interindividual- and sex-specific variations in the development of NAFLD. The severity of liver steatosis varied between sexes and individual strains and was accompanied by an elevation of serum markers of insulin resistance, including increases in total cholesterol, low-density lipoproteins, high-density lipoproteins, phospholipids, and glucose. The development of NAFLD was associated with overexpression of the critical fatty acid uptake and de novo lipogenesis genes Pparg, Mogat1, Cd36, Acaab1, Fabp2, and Gdf15 in male and female mice. The expression of Pparg, Mogat1, and Cd36 was positively correlated with liver triglycerides in male mice, and Mogat1 and Cd36 expression were positively correlated with liver triglycerides in female mice. Our results indicate the value of CC mice in combination with HF/HS diet-induced alterations as an approach to study the susceptibility and interindividual variabilities in the pathogenesis of nonalcoholic fatty liver and early nonalcoholic steatohepatitis at the population level, uncovering of susceptible and resistant cohorts, and identifying sex-specific molecular determinants of disease susceptibility.

From the Cover: Aloin, a Component of the Aloe Vera Plant Leaf, Induces Pathological Changes and Modulates the Composition of Microbiota in the Large Intestines of F344/N Male Rats

In a previous study, the oral administration of an Aloe vera whole leaf extract induced dose-related mucosal and goblet cell hyperplasia in the rat colon after 13 weeks and colon cancer after 2 years. The primary goal of this study was to determine whether or not the administration of aloin, a component of the Aloe vera plant leaf, would replicate the pathophysiological effects that were observed in rats in the previous study with an Aloe vera whole leaf extract. Groups of 10 male F344/N rats were administered aloin at 0, 6.95, 13.9, 27.8, 55.7, 111, 223, and 446 mg/kg drinking water for 13 weeks. At the end of study, rat feces were collected, and the composition of fecal bacteria was investigated by next generation sequencing of the PCR-amplified V3/V4 region of the 16S rRNA gene. At necropsy, blood was collected by cardiac puncture and organs and sections of the large intestine were collected for histopathology. Aloin induced dose-related increased incidences and severities of mucosal and goblet cell hyperplasia that extended from the cecum to the rectum, with increased incidences and severities detected at aloin doses ≥55.7 mg/kg drinking water. Analysis of the 16S rRNA metagenomics sequencing data revealed marked shifts in the structure of the gut microbiota in aloin-treated rats at each taxonomic rank. This study highlights the similarities in effects observed for aloin and the Aloe vera whole leaf extract, and points to a potential mechanism of action to explain the observed pathological changes via modulation of the gut microbiota composition.

Metabolic Disruption Early in Life is Associated With Latent Carcinogenic Activity of Dichloroacetic Acid in Mice

Early-life environmental factors can influence later-life susceptibility to cancer. Recent evidence suggests that metabolic pathways may mediate this type of latency effect. Previously, we reported that short-term exposure to dichloroacetic acid (DCA) increased liver cancer in mice 84 weeks after exposure was stopped. Here, we evaluated time course dynamics for key events related to this effect. This study followed a stop-exposure design in which 28-day-old male B6C3F1 mice were given the following treatments in drinking water for up to 93 weeks: deionized water (dH2O, control); 3.5 g/l DCA continuously; or 3.5 g/l DCA for 4-52 weeks followed by dH2O. Effects were evaluated at eight interim time points. A short-term biomarker study was used to evaluate DCA effects at 6, 15, and 30 days. Liver tumor incidence was higher in all DCA treatment groups, including carcinomas in 82% of mice previously treated with DCA for only 4 weeks. Direct effects of DCA in the short-term study included decreased liver cell proliferation and marked mRNA changes related to mitochondrial dysfunction and altered cell metabolism. However, all observed short-term effects of DCA were ultimately reversible, and prior DCA treatment did not affect liver cell proliferation, apoptosis, necrosis, or DNA sequence variants with age. Key intermediate events resulting from transient DCA exposure do not fit classical cytotoxic, mitogenic, or genotoxic modes of action for carcinogenesis, suggesting a distinct mechanism associated with early-life metabolic disruption.

Photo-co-carcinogenesis of Topically Applied Retinyl Palmitate in SKH-1 Hairless Mice

Cosmetic products that contain retinyl palmitate are popular as antiaging skin treatments; however, recent studies suggest a risk for enhanced skin tumor development with topical retinyl palmitate applications and exposure to solar ultraviolet radiation (UVR). In this study, we investigated the potential of retinyl palmitate to enhance UVR-induced photo-co-carcinogenesis. Groups of 36 male and 36 female SKH-1 hairless mice were exposed to simulated solar light (SSL) and treated with the control cream or creams containing retinyl palmitate, 5 days per week for 40 weeks. Other groups of mice were exposed to SSL and received no cream treatment or received cream treatments and were exposed to ultraviolet-A or ultraviolet-B. Mice were monitored for the development of skin tumors, and the incidences and multiplicities of squamous cell neoplasia were determined by histopathology. In both the absence and presence of SSL, mice administered the control cream developed skin tumors earlier and had higher incidences and multiplicities of skin squamous cell neoplasms than mice that received no cream treatment. Compared to the control cream groups, mice exposed to SSL and administered the retinyl palmitate creams demonstrated earlier onsets of skin tumors and had increased incidences and multiplicities of squamous cell skin neoplasms.

Low dose assessment of the carcinogenicity of furan in male F344/N Nctr rats in a 2-year gavage study

Furan is a volatile organic chemical that is a contaminant in many common foods. Furan is hepatocarcinogenic in mice and rats; however, the risk to humans from dietary exposure to furan cannot be estimated accurately because the lowest tested dose of furan in a 2-year bioassay in rats gave nearly a 100% incidence of cholangiocarcinoma. To provide bioassay data that can be used in preparing risk assessments, the carcinogenicity of furan was determined in male F344/N Nctr rats administered 0, 0.02, 0.044, 0.092, 0.2, 0.44, 0.92, and 2 mg furan/kg body weight (BW) by gavage 5 days/week for 2 years. Exposure to furan was associated with the development of malignant mesothelioma on membranes surrounding the epididymis and on the testicular tunics, with the increase being significant at 2 mg furan/kg BW. There was also a dose-related increase in the incidence of mononuclear cell leukemia, with the increase in incidence being significant at 0.092, 0.2, 0.92, and 2 mg furan/kg BW. Dose-related non-neoplastic liver lesions included cholangiofibrosis, mixed cell foci, basophilic foci, biliary tract hyperplasia, oval cell hyperplasia, regenerative hyperplasia, and cytoplasmic vacuolization. The most sensitive non-neoplastic lesion was cholangiofibrosis, the frequency of which increased significantly at 0.2 mg furan/kg BW.

Furan-induced transcriptomic and gene-specific DNA methylation changes in the livers of Fischer 344 rats in a 2-year carcinogenicity study

Furan is a significant food contaminant and a potent hepatotoxicant and rodent liver carcinogen. The carcinogenic effect of furan has been attributed to genotoxic and non-genotoxic, including epigenetic, changes in the liver; however, the mechanisms of the furan-induced liver tumorigenicity are still unclear. The goal of the present study was to investigate the role of transcriptomic and epigenetic events in the development of hepatic lesions in Fischer (F344) rats induced by furan treatment in a classic 2-year rodent tumorigenicity bioassay. High-throughput whole-genome transcriptomic analysis demonstrated distinct alterations in gene expression in liver lesions induced in male F344 rats treated with 0.92 or 2.0 mg furan/kg body weight (bw)/day for 104 weeks. Compared to normal liver tissue, 1336 and 1541 genes were found to be differentially expressed in liver lesions in rats treated with 0.92 and 2.0 mg furan/kg bw/day, respectively, among which 1001 transcripts were differentially expressed at both doses. Pairing transcriptomic and next-generation bisulfite sequencing analyses of the common differentially expressed genes identified 42 CpG island-containing genes in which the methylation level was correlated inversely with gene expression. Forty-eight percent of these genes (20 genes, including Areg, Jag1, and Foxe1) that exhibited the most significant methylation and gene expression changes were involved in key pathways associated with different aspects of liver pathology. Our findings illustrate that gene-specific DNA methylation changes have functional consequences and may be an important component of furan hepatotoxicity and hepatocarcinogenicity.

Subchronic Toxicity of 1,3,5-Trinitrobenzene in Fischer 344 Rats

The subchronic toxicity of 1,3,5-trinitrobenzene (TNB) in male and female Fischer 344 rats was evaluated by feeding a powdered certified laboratory diet containing 0, 66.7, 400 and 800 mg TNBl kg diet for 90 days. The calculated average TNB intake was 4.29, 24.70, and 49.28 mg/kg body weight (BW)day for females and 3.91, 22.73, and 44.16 mg/ kg BWI day for males. Food intake in the 400 and 800 mg/kg diet dose groups of both sexes was decreased throughout the study and resulted in a significant decrease in absolute body weights. A significant decrease in relative testicular weights and a significant increase in the relative liver weight were observed in male rats receiving 400 or 800 mg TNB/kg diet. A significant increase in the relative spleen weights of both sexes receiving 400 or 800 mg TNB diet was noted. The relative liver weight was also increased only in female rats maintained on the 800 mg TNB diet. Histopathological examinations revealed that the susceptible organs for TNB toxicity were kidney (hyaline droplets) in all male dose groups and testes (seminiferous tubular degeneration) in rats receiving 400 and 800 mg TNB diet groups. The spleen was also affected (extramedullary hematopoiesis) in both sexes in the 400 and 800 mg dose groups. Hematological studies at both 45 (data not given) and 90 days in the 400 and 800 mg dose groups indicated decreased values for red blood cell counts and hemoglobin content, while reticulocytes and methemoglobin levels were increased. Clinical chemistry parameters were unaffected. Based on kidney toxicity and hematological effects, a Low Observed Adverse Effect Level (LOAEL) of 3.91 mg/kg BWI day was suggested for subchronic toxicity studies on TNB.

Toxicity of Tetryl (N-Methyl-N,2,4,6–Tetranitroaniline) in F344 Rats

The toxicity of tetryl (N-methyl-N,2,4,6–tetranitroaniline) in male and female F344 rats was evaluated after adminstration in the diet for 14 or 90 days. The 14–day study diet concentrations used were 0, 500, 1250, 2000, 2500, and 5000 ppm; the 90–day study diet concentrations were 0, 200, 1000, and 3000 ppm tetryl in the diet. The calculated average daily tetryl intake was 32.1, 82.5, 130.3, 178.9, and 374.4 mg/kg body weight (BW) for females and 31.8, 80.0, 121.0, 170.5, and 349.7 mg/kg BW for males in the 14–day study. For the 90–day studies, the daily tetryl intake was 14.2, 68.8, and 199.0 mg/kg BW for females and 13.0, 62.4, and 179.6 mg/kg BW for males. In the 14–day study, there was a significant decrease in body weights (males), whereas relative(organ/body weight) liver and spleen (females), and kidney (males) weights were significantly increased in the 5000–ppm dose group. Hematological effects observed were decreased hemoglobin and hematocrit and an increased number of reticulocyts in females (2000 to 5000 ppm). Methemoglobin levels in males (2000 to 5000 ppm) and females (5000 ppm) and total blood protein and albumin levels in all groups of males and females (except 500 ppm) were significantly increased. Histopathological changes were observed in kidneys (deposition of cytoplasmic droplets) of all dose groups of male rats. In the sub–chronic (90–day) study, feed intake was reduced in all dose groups, but a significant decrease in terminal body weights was observed in females (1000 and 3000 ppm) and males (3000 ppm). An increase in the relative liver, kidney (1000–3000 ppm), and spleen (3000 ppm) weights were noted in both sexes. The hemoglobin content and red blood cell count were decreased whereas the reticulocyte count was elevated (3000 ppm) in both sexes at 45 and 90 days. Methemoglobin levels were increased in both sexes (1000 and 3000 ppm). Histopathologicalchanges were noted in the spleen (pigment deposition and erythroid cell hyperplasia) of both sexes (3000 ppm) and kidneys (tubular degeneration and cytoplasmic droplets containing alpha-2-micro globulin) of male rats (1000 to 3000 ppm). A no observed adverse effect level (NOAEL) for both sexes was 13 mg/kg BW/day was determined.

Differential Effects of Silver Nanoparticles and Silver Ions on Tissue Accumulation, Distribution, and Toxicity in the Sprague Dawley Rat Following Daily Oral Gavage Administration for 13 Weeks

There are concerns within the regulatory and research communities regarding the health impact associated with consumer exposure to silver nanoparticles (AgNPs). This study evaluated particulate and ionic forms of silver and particle size for differences in silver accumulation, distribution, morphology, and toxicity when administered daily by oral gavage to Sprague Dawley rats for 13 weeks. Test materials and dose formulations were characterized by transmission electron microscopy (TEM), dynamic light scattering, and inductively coupled mass spectrometry (ICP-MS). Seven-week-old rats (10 rats per sex per group) were randomly assigned to treatments: AgNP (10, 75, and 110 nm) at 9, 18, and 36 mg/kg body weight (bw); silver acetate (AgOAc) at 100, 200, and 400 mg/kg bw; and controls (2 mM sodium citrate (CIT) or water). At termination, complete necropsies were conducted, histopathology, hematology, serum chemistry, micronuclei, and reproductive system analyses were performed, and silver accumulations and distributions were determined. Rats exposed to AgNP did not show significant changes in body weights or intakes of feed and water relative to controls, and blood, reproductive system, and genetic tests were similar to controls. Differences in the distributional pattern and morphology of silver deposits were observed by TEM: AgNP appeared predominantly within cells, while AgOAc had an affinity for extracellular membranes. Significant dose-dependent and AgNP size-dependent accumulations were detected in tissues by ICP-MS. In addition, sex differences in silver accumulations were noted for a number of tissues and organs, with accumulations being significantly higher in female rats, especially in the kidney, liver, jejunum, and colon.

Carcinogenicity of glycidamide in B6C3F1 mice and F344/N rats from a two-year drinking water exposure

Acrylamide is a contaminant in baked and fried starchy foods, roasted coffee, and cigarette smoke. Previously we reported that acrylamide is a multi-organ carcinogen in B6C3F1 mice and F344/N rats, and hypothesized that acrylamide is activated to an ultimate carcinogen through metabolism to the epoxide glycidamide. We have now examined the carcinogenic effects of glycidamide administered at 0, 0.0875, 0.175, 0.35 and 0.70 mM in drinking water to the same strains of rodents for two years. In male and female mice, there were significant increases in tumors of the Harderian gland, lung, forestomach, and skin. Female mice also had an increased incidence of tumors of the mammary gland and ovary. In male and female rats, there were significant increases in thyroid gland and oral cavity neoplasms and mononuclear cell leukemia. Male rats also had increases in tumors of the epididymis/testes and heart, while female rats demonstrated increases in tumors of the mammary gland, clitoral gland, and forestomach. A similar spectrum of tumors was obtained in mice and rats administered acrylamide. These data indicate that, under the conditions of these bioassays, acrylamide is efficiently metabolized to glycidamide and that the carcinogenic activity of acrylamide is due to its conversion into glycidamide.

Utilizing Whole Slide Images for Pathology Peer Review and Working Groups

This article describes the results of comparisons of digitally scanned whole slide images (WSIs) and glass microscope slides for diagnosis of tissues under peer review by the National Toxicology Program. Findings in this article were developed as a result of the data collected from 6 pathology working groups (PWGs), 1 pathology peer review, and survey comments from over 25 participating pathologists. For each PWG, 6-14 pathologists examined 10-143 tissues per study from 6- and 9-month perinatal studies and 2-year carcinogenicity studies. Overall it was found that evaluation of WSIs is generally equivalent to using glass slides. Concordance of PWG consensus diagnoses based upon review of WSIs versus glass slides ranged from 74% to 100% (median 86%). The intra- and interobserver diagnostic variation did not appear to influence the conclusions of any study. Based upon user opinions collected from surveys, WSIs may be less optimal than glass slides for evaluation of subtle lesions, large complex lesions, small lesions in a large section of tissue, and foci of altered hepatocytes. These results indicate that, although there may be some limitations, the use of WSIs can effectively accomplish the objectives of a conventional glass slide review and definitely serves as a useful adjunct to the conduct of PWGs.

Dose–response assessment of the dermal toxicity of triclosan in B6C3F1 mice

Triclosan [5-chloro-2-(2,4-dichlorophenoxy)phenol] is a widely used antimicrobial agent in personal care products, household items, medical devices, and clinical settings.

Comparative time course profiles of phthalate stereoisomers in mice

More efficient models are needed to assess potential carcinogenicity hazard of environmental chemicals based on early events in tumorigenesis. Here, we investigated time course profiles for key events in an established cancer mode of action. Using a case study approach, we evaluated two reference phthalates, di(2-ethylhexyl) phthalate (DEHP) and its stereoisomer di-n-octyl phthalate (DNOP), across the span of a two-year carcinogenicity bioassay. Male B6C3F1 mice received diets with no phthalate added (control), DEHP at 0.12, 0.60, or 1.20%, or DNOP at 0.10, 0.50, or 1.00% (n = 80-83/group) for up to 104 weeks with six interim evaluations starting at week 4. Mean phthalate doses were 139, 845, and 3147 mg/kg/day for DEHP and 113, 755, and 1281 mg/kg/day for DNOP groups, respectively. Incidence and number of hepatocellular tumors (adenoma and/or carcinoma) were greater at ≥ 60 weeks for all DEHP groups with time and dose trends, whereas DNOP had no significant effects. Key events supported a peroxisome proliferator-activated receptor alpha (PPARα) mode of action for DEHP, with secondary cytotoxicity at the high dose, whereas DNOP induced modest increases in PPARα activity without proliferative or cytotoxic effects. Threshold estimates for later tumorigenic effects were identified at week 4 for relative liver weight (+24%) and PPARα activity (+79%) relative to the control group. Benchmark doses (BMDs) for these measures at week 4 clearly distinguished DEHP and DNOP and showed strong concordance with values at later time points and tumorigenic BMDs. Other target sites included testis and kidney, which showed degenerative changes at higher doses of DEHP but not DNOP. Our results highlight marked differences in the chronic toxicity profiles of structurally similar phthalates and demonstrate quantitative relationships between early bioindicators and later tumor outcomes.

Toxicity evaluation of bisphenol A administered by gavage to Sprague Dawley rats from gestation day 6 through postnatal day 90

Bisphenol A (BPA) is a high production volume industrial chemical to which there is widespread human oral exposure. Guideline studies used to set regulatory limits detected adverse effects only at doses well above human exposures and established a no-observed-adverse-effect level (NOAEL) of 5 mg/kg body weight (bw)/day. However, many reported animal studies link BPA to potentially adverse effects on multiple organ systems at doses below the NOAEL. The primary goals of the subchronic study reported here were to identify adverse effects induced by orally (gavage) administered BPA below the NOAEL, to characterize the dose response for such effects and to determine doses for a subsequent chronic study. Sprague Dawley rat dams were dosed daily from gestation day 6 until the start of labor, and their pups were directly dosed from day 1 after birth to termination. The primary focus was on seven equally spaced BPA doses (2.5-2700 μg/kg bw/day). Also included were a naïve control, two doses of ethinyl estradiol (EE2) to demonstrate the estrogen responsiveness of the animal model, and two high BPA doses (100,000 and 300,000 μg/kg bw/day) expected from guideline studies to produce adverse effects. Clear adverse effects of BPA, including depressed gestational and postnatal body weight gain, effects on the ovary (increased cystic follicles, depleted corpora lutea, and antral follicles), and serum hormones (increased serum estradiol and prolactin and decreased progesterone), were observed only at the two high doses of BPA. BPA-induced effects partially overlapped those induced by EE2, consistent with the known weak estrogenic activity of BPA.

Clear evidence of carcinogenic activity by a whole-leaf extract of Aloe barbadensis miller (aloe vera) in F344/N rats

Aloe barbadensis Miller (Aloe vera) is an herbal remedy promoted to treat a variety of illnesses; however, only limited data are available on the safety of this dietary supplement. Drinking water exposure of F344/N rats and B6C3F1 mice to an Aloe vera whole-leaf extract (1, 2, and 3%) for 13 weeks resulted in goblet cell hyperplasia of the large intestine in both species. Based upon this observation, 2-year drinking water studies were conducted to assess the carcinogenic potential of an Aloe vera whole-leaf extract when administered to F344/N rats (48 per sex per group) at 0.5, 1, and 1.5%, and B6C3F1 mice (48 per sex per group) at 1, 2, and 3%. Compared with controls, survival was decreased in the 1.5% dose group of female rats. Treatment-related neoplasms and nonneoplastic lesions in both species were confined primarily to the large intestine. Incidences of adenomas and/or carcinomas of the ileo-cecal and cecal-colic junction, cecum, and ascending and transverse colon were significantly higher than controls in male and female rats in the 1 and 1.5% dose groups. There were no neoplasms of the large intestine in mice or in the 0 or 0.5% dose groups of rats. Increased incidences of mucosa hyperplasia of the large intestine were observed in F344/N rats, and increased incidences of goblet cell hyperplasia of the large intestine occurred in B6C3F1 mice. These results indicate that Aloe vera whole-leaf extract is an intestinal irritant in F344/N rats and B6C3F1 mice and a carcinogen of the large intestine in F344/N rats.

Aloe vera non-decolorized whole leaf extract-induced large intestinal tumors in F344 rats share similar molecular pathways with human sporadic colorectal tumors

Aloe vera is one of the most commonly used botanicals for various prophylactic and therapeutic purposes. Recently, NTP/NCTR has demonstrated a dose-dependent increase in large intestinal tumors in F344 rats chronically exposed to Aloe barbadensis Miller (Aloe vera) non-decolorized whole leaf extract (AVNWLE) in drinking water. The morphological and molecular pathways of AVNWLE-induced large intestinal tumors in the F344 rats were compared to human colorectal cancer (hCRC) literature. Defined histological criteria were used to compare AVNWLE-induced large intestinal tumors with hCRC. The commonly mutated genes (Kras, Ctnnb1, and Tp53) and altered signaling pathways (MAPK, WNT, and TGF-β) important in hCRC were evaluated within AVNWLE-induced large intestinal tumors. Histological evaluation of the large intestinal tumors indicated eight of twelve adenomas (Ads) and four of twelve carcinomas (Cas). Mutation analysis of eight Ads and four Cas identified point mutations in exons 1 and 2 of the Kras gene (two of eight Ads, two of four Cas), and in exon 2 of the Ctnnb1 gene (three of eight Ads, one of four Cas). No Tp53 (exons 5-8) mutations were found in Ads or Cas. Molecular pathways important in hCRC such as MAPK, WNT, and TGF-β signaling were also altered in AVNWLE-induced Ads and Cas. In conclusion, the AVNWLE-induced large intestinal tumors in F344 rats share several similarities with hCRC at the morphological and molecular levels.

Dose-response assessment of nephrotoxicity from a 7-day combined exposure to melamine and cyanuric acid in F344 rats

The intentional adulteration of pet food with melamine and derivatives, including cyanuric acid, has been implicated in the kidney failure and death of a large number of cats and dogs in the United States. Although individually these compounds present low toxicity, coexposure can lead to the formation of melamine cyanurate crystals in the nephrons and eventual kidney failure. To determine the dose-response for nephrotoxicity upon coadministration of melamine and cyanuric acid, groups of male and female F344 rats (six animals per sex per group) were fed 0 (control), 7, 23, 69, 229, or 694 ppm of both melamine and cyanuric acid; 1388 ppm melamine; or 1388 ppm cyanuric acid in the diet for 7 days. No toxicity was observed in the rats exposed to the individual compounds, whereas anorexia and a statistically significant increase in blood urea nitrogen and serum creatinine levels was observed in the animals treated with 229 and 694 ppm melamine and cyanuric acid. The kidneys of these animals were grossly enlarged and pale yellow. Large numbers of crystalline structures deposited in the tubules were seen on sections in kidneys from all rats in these treatment groups. No significant changes were detected in the remaining treatment groups exposed to both melamine and cyanuric acid. In the melamine-only treatment group, 5 of 12 rats had scattered crystals present in renal tubules when examined by wet mount. These were not observed by histopathology. The observed adverse effect level (8.6 mg/kg bw [body weight]/day) and benchmark dose modeling data (8.4-10.9 mg/kg bw/day) determined in this study suggest that the tolerable daily intake values derived from studies conducted with melamine alone may underestimate the risk from coexposures to melamine and cyanuric acid.

Carcinogenicity of bromodichloromethane administered in drinking water to Male F344/N Rats and B6C3F1 mice

A life-time exposure study was conducted to assess the carcinogenicity of bromodichloromethane (BDCM) administered in the drinking water to male F344/N rats and B6C3F(1) mice. In mouse, the calculated mean daily BDCM concentrations (measured concentrations corrected for on-cage loss of chemical) were 0.06, 0.28 and 0.49 g/l. Time-weighted water consumption of 135, 97, and 89 ml/kg/day resulted in mean daily doses of 8.1, 27.2, and 43.4 mg BDCM/kg/day. No changes in feed consumption, final body weight, or survival were observed. Kidney weights were significantly depressed at 27.2 and 43.4 mg BDCM/kg/day. There was no increase in neoplasia in the liver, kidney, spleen, testis, bladder, sections along the alimentary tract, excised lesions, or at any other organ site. In rat, the corrected mean daily BDCM concentrations were 0.06, 0.33, and 0.62 g/l. Time-weighted water consumption of 65, 63, and 59 ml/kg/day yielded 3.9, 20.6 and 36.3 mg BDCM/kg/day. No alterations in feed consumption, body weight gain, and survival were seen. Kidney weight was significantly depressed in the 36.3-mg/kg/day treatment group. There was a significantly enhanced prevalence and multiplicity of hepatocellular adenomas at 3.9 mg BDCM/kg/day (15.5% and 0.16/animal vs. 2.2% and 0.02/animal for the control). Hepatocellular carcinomas increased from 2.2% and 0.02/animal for the control and 3.9 mg BDCM/kg/day to 8.3% and 0.10/animal at 20.6 mg BDCM/kg/day. The combined neoplasms were enhanced at 3.9 and 20.6 mg BDCM/kg/day. Liver neoplasia was depressed to the control value at 36.3 mg BDCM/kg. The prevalence of basophilic and clear cell, but not eosinophilic cells, altered foci of cells declined with increasing dose. BDCM did not increase cancer in the large bowel, renal tubules, or in any of the other tissues examined. Renal tubular hyperplasia was observed at 36.3 mg BDCM/kg (15.8% vs. 8.7% for the control group). Under the conditions of the study, BDCM in the drinking water was not carcinogenic in the male B6C3F(1) mouse, but was carcinogenic in the male F344/N rat based on an increased hepatocellular neoplasia.

Chronic toxicity of 1,3,5-trinitrobenzene in Fischer 344 rats

The chronic toxicity of 1,3,5-trinitrobenzene (TNB) in male and female Fischer 344 (F344) rats was evaluated by feeding a diet containing 0, 5, 60, and 300 ppm of TNB for 2 years. The calculated average TNB intake over 2 years for males and females was 0.22, 2.64, 13.44 and 0.23, 2.68, 13.31 mg/kg body weight (BW)/day respectively. Terminal body weights were decreased and water intake was increased in both sexes (300 ppm), whereas food consumption was decreased in males (60 and 300 ppm groups) only. The relative spleen weights were significantly decreased in both sexes (300 ppm), whereas the relative brain weights were increased in females only (300 ppm). Hematological effects were not observed in animals killed at the 2-year time point, except significant decrease in the mean corpuscular hemoglobin (MCH) in males (300 ppm) and in females (60 and 300 ppm). Methemoglobin levels were increased in both sexes in the high dose group. Histopathological examination showed treatment-related changes in the kidney (hyaline droplets; 60 and 300 ppm) and the spleen (erythroid cell hyperplasia and pigment deposition; 300 ppm) of both sexes. Cytoplasmic hyaline droplets in the kidneys were characterized by immunohistochemistry as alpha-2mu-globulin. We propose a chronic, oral no-observable-adverse-effect level (NOAEL) of 2.68 mg/kg BW/day for TNB in the rat, based on the hematological and renal changes.

Chronic Toxicity of 1,3,5-Trinitrobenzene in Fischer 344 Rats

The chronic toxicity of 1,3,5-trinitrobenzene (TNB) in male and female Fischer 344 (F344) rats was evaluated by feeding a diet containing 0, 5, 60, and 300 ppm of TNB for 2 years. The calculated average TNB intake over 2 years for males and females was 0.22, 2.64,13.44 and 0.23, 2.68, 13.31 mg/kg body weight (BW)/day respectively. Terminal body weights were decreased and water intake was increased in both sexes (300 ppm), whereas food consumption was decreased in males (60 and 300 ppm groups) only. The relative spleen weights were significantly decreased in both sexes (300 ppm), whereas the relative brain weights were increased in females only (300 ppm). Hematological effects were not observed in animals killed at the 2-year time point, except significant decrease in the mean corpuscular hemoglobin (MCH) in males (300 ppm) and in females (60 and 300 ppm). Methemoglobin levels were increased in both sexes in the high dose group. Histopathological examination showed treatment-related changes in the kidney (hyaline droplets; 60 and 300 ppm) and the spleen (erythroid cell hyperplasia and pigment deposition; 300 ppm) of both sexes. Cytoplasmic hyaline droplets in the kidneys were characterized by immunohistochemistry as alpha-2μ-globulin. We propose a chronic, oral no-observable-adverse-effect level (NOAEL) of 2.68 mg/kg BW/day for TNB in the rat, based on the hematological and renal changes.

Carcinogenicity of chloral hydrate administered in drinking water to the male F344/N rat and male B6C3F1 mouse

Male B6C3F1 mice and male F344/N rats were exposed to chloral hydrate (chloral) in the drinking water for 2 years. Rats: Measured chloral hydrate drinking water concentrations for the study were 0.12 g/L, 0.58 g/L, and 2.51 g/L chloral hydrate that yielded time-weighted mean daily doses (MDDs) of 7.4, 37.4, and 162.6 mg/kg per day. Water consumptions, survival, body weights, and organ weights were not altered in any of the chloral hydrate treatments. Life-time exposures to chloral hydrate failed to increase the prevalence (percentage of animals with a tumor) or the multiplicity (tumors/animal) of hepatocellular neoplasia. Chloral hydrate did not increase the prevalence of neoplasia at any other organ site. Mice: Measured chloral hydrate drinking water concentrations for the study were 0.12 g/L, 0.58 g/L, and 1.28 g/L that gave MDDs of 13.5, 65.0, and 146.6 mg/kg per day. Water consumptions, survival, body and organ weights, were not altered from the control values by any of the chloral hydrate treatments. Enhanced neoplasia was observed only in the liver. Prevalence and multiplicity of hepatocellular carcinoma (HC) were increased only for the high-dose group (84.4%; 0.72 HC/animal; p < or = 0.05). Values of 54.3%; 0.72 HC/animal and 59%; 1.03 HC/animal were observed for the 13.5- and 65.0-mg/kg per day treatment groups. Prevalence and multiplicity for the control group were 54.8%; 0.74 HC/animal. Hepatoadenoma (HA) prevalence and multiplicity were significantly increased (p < or = 0.05) at all chloral hydrate concentrations: 43.5%; 0.65 HA/animal, 51.3%; 0.95 HA/animal and 50%; 0.72 HA/animal at 13.5, 65.0, and 146.6 mg/kg per day chloral hydrate compared to 21.4%; 0.21 HA/animal in the untreated group. Altered foci of cells were evident in all doses tested in the mouse, but no significant differences were observed over the control values. Hepatocellular necrosis was minimal and did not exceed that seen in untreated rats and mice. Chloral hydrate exposure did not alter serum chemistry and hepatocyte proliferation in rats and mice or increase hepatic palmitoyl CoA oxidase in mice at any of the time periods monitored. It was concluded that chloral hydrate was carcinogenic (hepatocellular neoplasia) in the male mouse, but not in the rat, following a lifetime exposure in the drinking water. Based upon the increased HA and combined tumors at all chloral hydrate doses tested, a no observed adverse effect level was not determined.

Failure of monochloroacetic acid and trichloroacetic acid administered in the drinking water to produce liver cancer in male F344/N rats

The chlorinated acetic acids monochloroacetic acid (MCA) and trichloroacetic acid (TCA) are found as chlorine disinfection by-products in finished drinking-water supplies. TCA has been demonstrated to be a mouse liver carcinogen. A chronic study in which male Fischer 344/N rats were exposed for 104 wk to TCA and MCA in the drinking water is described. Animals, 28 d old, were exposed to 0.05, 0.5, or 2 g/L MCA, or 0.05, 0.5, or 5 g/L TCA. The 2.0 g/L MCA was lowered in stages to 1 g/L when the animals began to exhibit signs of toxicity. A time-weighted mean daily MCA concentration (MDC) of 1.1 g/L was calculated over the 104-wk exposure period. Time-weighted mean daily doses (MDD) based upon measured water consumption were 3.5, 26.1, and 59.9 mg/kg/d for 0.05, 0.5, and 1.1 g/L MCA, respectively; TCA MDD were 3.6, 32.5, and 363.8 mg/kg/d. Nonneoplastic hepatic changes were for the most part spontaneous and age related. No evidence of hepatic neoplasia was found at any of the MCA or TCA doses. The incidence of neoplastic lesions at other sites was not enhanced over that in the control group. Drinking water concentrations of > or = 0.5 g/L MCA produced a moderate to severe toxicity as reflected by a depressed water consumption and growth rate. A no-observed-effects level (NOEL) for carcinogenicity of 0.5 g/L (26.1 mg/kg/d) MCA was calculated. TCA at drinking water levels as high as 5 g/L produced only minimal toxicity and growth inhibition and provided a NOEL of 364 mg/kg/d. Our results demonstrate that under the conditions of this bioassay, MCA and TCA were not tumorigenic in the male F344/N rat.

The carcinogenicity of dichloroacetic acid in the male Fischer 344 rat

The chlorinated acetic acids, in particular dichloroacetic acid (DCA), are found as chlorine disinfection by-products in finished drinking water supplies. DCA has previously been demonstrated to be a mouse liver carcinogen. Chronic studies are described in which male Fischer (F344) rats were exposed to DCA in their drinking water. In the first study, 28 day old rats were exposed to a regimen of 0.05, 0.5 and 5.0 g/l DCA. When animals in the high dose group began to exhibit peripheral hind leg neuropathy, the dose was lowered in stages to 1 g/l. These animals were sacrificed at 60 weeks due to the severe, irreversible neuropathy and were not included in this analysis. The remaining groups of animals were treated for 100 weeks. In the second study, rats were initially exposed to 2.5 g/l DCA which was lowered to 1 g/l after 18 weeks. The mean daily concentration (MDC) of 1.6 g/l was calculated over the 103 week exposure period. Time-weighted mean daily doses (MDD) based on measured water consumption were 3.6, 40.2 and 139 mg/kg bw/day for the 0.05, 0.5 and 1.6 g/l DCA respectively. Based upon the pathologic examination, DCA induced observable signs of toxicity in the nervous system, liver and myocardium. However, treatment related neoplastic lesions were observed only in the liver. A statistically significant increase of carcinogenicity (hepatocellular carcinoma) was noted at 1.6 g/l DCA. Exposure to 0.5 g/l DCA increased-hepatocellular neoplasia, (carcinoma and adenoma) at 100 weeks. These data demonstrate that DCA is an hepatocarcinogen to the male F344 rat. Calculation of the MDD at which 50% of the animals exhibited liver neoplasia indicated that the F344 male rat (approximately 10 mg/kg bw/day) is ten times more sensitive than the B6C3F1 male mouse (approximately 100 mg/kg bw/day). A "no observed effects level' (NOEL) of 0.05 g/l (3.6 mg/kg/day) was the same as for the mouse (3-8 mg/kg/day).

Fourteen-day toxicity study of 1,3,5-trinitrobenzene in Fischer 344 rats

Toxic effects of 1,3,5-trinitrobenzene (TNB) in male and female rats were evaluated by feeding powdered certified laboratory chow diet supplemented with varied concentrations of TNB (0, 50, 200, 400, 800 and 1200 mg kg-1 diet) for 14 days. Food intake by female rats in 400, 800 and 1200 mg TNB diet groups was reduced and resulted in a significant decrease in absolute body weights (BW). Food and water consumption by male rats in high-dose groups (800 and 1200 mg TNB kg-1 diet) was also reduced and resulted in a significant decrease in body weight. The calculated average TNB intake (from 1200 mg TNB kg-1 diet) was 92 mg kg-1 BW day-1 for male rats and 80 mg kg-1 BW day-1 for females. A decrease in testicular weight in males and an increase in spleen weight of both sexes in high-dose groups was noted. In addition, histopathological examinations revealed that the susceptible organs for TNB toxicity were kidney (hyaline droplets), spleen (extramedullary hematopoiesis), brain (hemorrhage, malacia and gliosis) and testes (seminiferous tubular degeneration). Hematology and clinical chemistry studies indicated a decrease in red blood cell count and hematocrit, a decrease in alkaline phosphatase, an increase in Heinz bodies and increased methemoglobin concentration as compared to controls in both sexes. A lowest observed adverse effect level of 4.41 mg TNB kg-1 BW day-1 was established based on the findings of this study.

Effects of the phytochemicals, curcumin and quercetin, upon azoxymethane-induced colon cancer and 7,12-dimethylbenz[a]anthracene-induced mammary cancer in rats

Curcumin and quercetin were evaluated in rats for their ability to modulate the carcinogenic activity of azoxymethane (AOM) in the colon and 7,12-dimethylbenz[a]anthracene (DMBA) in the mammary gland. In the AOM-induced colon cancer model, male Fischer 344 rats at 8 weeks of age started to receive either curcumin (8 and 16 g/kg) or quercetin (16.8 and 33.6 g/kg) in the diet and 1 week later, were administered AOM (30 mg/kg body wt.) by subcutaneous injection. The animals continued to receive the two agents in the diet until sacrificed 45 weeks later. Curcumin mediated a dose-dependent inhibition of the incidence and multiplicity of adenomas from 47% and 0.58 +/- 0.12 adenomas/rat in the AOM-treated control group to 19% and 0.22 +/- 0.08 and 0.06% and 0.08 +/- 0.06 adenomas/rat for the low and high dose groups, respectively. A low yield of adenocarcinomas (0.06 +/- 0.04 adenocarcinomas/rat) was induced by AOM which was not significantly altered by curcumin. Treatment with quercetin caused a dose-dependent increase in the yield of AOM-induced tumors in the colon from 0.06 +/- 0.04 adenocarcinoma/rat to 0.64 +/- 0.12 and 1.14 +/- 0.17 for the low and high dose groups, respectively. In the DMBA-induced mammary cancer model, curcumin or quercetin was administered at either 10 or 20 g/kg diet, beginning 7 days prior to DMBA and continually throughout the remainder of the experiment. Neither curcumin nor quercetin significantly altered the incidence of animals with tumors or the tumor multiplicity, while the high concentration of both agents significantly increased tumor latency. These results demonstrate different responses to these agents in the two models. While curcumin was highly effective as a chemopreventive agent in the colon model, it was only weakly effective in the mammary model. In contrast, quercetin which was also only weakly effective in the mammary model, caused a dose-dependent enhancement of tumors induced by AOM in the colon model.

Toxicity studies of epichlorohydrin in Sprague-Dawley rats

Adult male and female Sprague-Dawley rats received epichlorohydrin via gavage in distilled water for 10 consecutive days at dose levels of 3, 7, 19, and 46 mg/kg-day, and for 90 days at dose levels of 1, 5, and 25 mg/kg-day. Epichlorohydrin did not adversely effect mortality, but toxicity, at the higher doses, was evident by: 1) losses in body weight gain and organ weights, 2) reductions in food and water consumption, and 3) in the hematological and microscopic examinations in both study periods. Significant decreases in erythrocyte count, hemoglobin, and hematocrit levels were found in the high dose level in males after 10 and 90 days. Dose-related increases in kidney and liver weights were observed in both sexes at 25 mg/kg-day in the 90-day study and in various organs for both 19 and 46 mg/kg-day in the 10-day study. Histopathological examination identified the forestomach as the primary target organ for both sexes and in both studies with significant dose-related increases in mucosal hyperplasia (acanthosis) and hyperkeratosis. Based on the data presented, a lowest observable adverse effect level (LOAEL) for oral exposure of Sprague-Dawley rats to epichlorohydrin is 3 mg/kg-day for 10 days and 1 mg/kg-day is suggested as the no observed adverse effect level (NOAEL) for a 90 day oral exposure. These conclusions were the same whether the lesions were analyzed for each sex individually or whether the data in each study was pooled.

The effects of subacute and subchronic oral exposure to cis-1,2-dichloroethylene in Sprague-Dawley rats

Cis-1,2-dichloroethylene was administered daily by corn oil gavage to male and female Sprague-Dawley rats at the following dose levels: 1.0, 3.0, 10.0 and 22.0 mmol/kg/day for 14 days. Doses gavaged during the 90-day subchronic study were 0.33, 1.00, 3.00 and 9.00 mmol/kg/day. There were no compound-related deaths or histopathological changes demonstrated. Significant increases in relative liver weights were seen after 14- and 90-days of treatment in both sexes. This study demonstrates some indication of toxicity at subacute and subchronic exposure levels as low as 0.33 mmol/kg/day. Implications of liver abnormalities were demonstrated at an exposure level of 1 mmol/kg/day while kidney abnormalities (relative weights) were demonstrated at an exposure level of 0.33 mmol/kg/day.

Toxicity studies of 1,3-dichlorobenzene in Sprague-Dawley rats

Male and female Sprague-Dawley rats received 1,3-dichlorobenzene daily by corn oil gavage for 10 or 90 consecutive days. The 10-day study doses were 0, 37, 147, 368 and 735 mg/kg; the 90-day study doses were 0, 9, 37, 147 and 588 mg/kg. In the 10-day study, there was a significant depression of body weight in both sexes at 735 mg/kg. Liver weights were significantly increased in both sexes at 368 and 735 mg/kg. Serum cholesterol levels were significantly elevated in both sexes at 368 and 735 mg/kg. Histopathological evaluation revealed centrolobular hepatocellular degeneration at 368 mg/kg in males and 735 mg/kg in females. In the 90-day study, body weights were significantly depressed in both sexes at 588 mg/kg. Normalization of food and water consumption by final body weight indicated that at 588 mg/kg both sexes had increased food and water consumption relative to controls. Absolute and relative liver weights were significantly increased in both sexes at 147 and 588 mg/kg. Relative kidney weights were significantly higher in both sexes at 588 mg/kg and in males at 147 mg/kg. Serum cholesterol and calcium levels were significantly elevated over controls in females at 37, 147, and 588 mg/kg, and in males at all dose levels. Histopathological evaluation at 147 and/or 588 mg/kg demonstrated liver and thyroid lesions in both sexes, and pituitary and kidney lesions in males. A NOAEL was not firmly established.

The effects of subchronic chlorate exposure in Sprague-Dawley rats

Male and female Sprague-Dawley rats were exposed to drinking water containing 3.0, 12.0 or 48.0 mM sodium chlorate. The mean drinking water consumption varied between exposure groups from 100-200 ml/kg/day. Female exposure groups consistently drank more water (23-42%) than male exposure groups thereby receiving more chlorate/kg/day at every exposure level. There were no compound related deaths; however, both males and females in the high exposure groups had significant weight loss during the 90-day exposure period. Also, in these same groups females had mild but significant decreases in the following relative organ weights; adrenals, thymus and spleen, while the relative brain weight was increased. In males, the heart, kidneys and liver were mildly decreased while the brain and testes were mildly increased. Red blood cell counts and percent hematocrit were decreased in both sexes in the high dose group. Pituitary gland (pars distalis) vacuolization and thyroid gland colloid depletion were prominent in both sexes in mid and/or high dose animals. A NOAEL of 0.36 mM chlorate/kg b.w./day in males and 0.50 mM chlorate/kg b.w./day in females were established.

Ten and ninety-day toxicity studies of 1,2-dichloroethane in Sprague-Dawley rats

Male and female Sprague-Dawley rats received 1,2-dichloroethane in corn oil by gavage for 10 or 90 consecutive days. The doses for the 10-day study were 10, 30, 100, and 300 mg/kg; the 90-day study doses were 37.5, 75, and 150 mg/kg. There were ten animals per sex per dose group. In the 10-day study, all female animals died in the high dose group and only 2 of 10 males survived. Final body weights and weight gain along with hematology and clinical chemistry findings were not different from controls. The only relative organ weight which was significantly different was the liver in males exposed to 100 mg/kg. The main histopathological lesion exhibited was multifocal to diffuse inflammation of the mucosal and submucosal layers of the forestomach in the 100 mg/kg dose group. This change was minimal in both males and females. In the 90-day study there were no treatment-related effects pertaining to clinical observations. Body weight gain and total food consumption were significantly decreased in high dose males. There were slight but significant differences in hemoglobin, hematocrit, red blood cell count, platelets, albumin, and alkaline phosphatase values in the 75 and/or 150 mg/kg groups in one or both sexes. In males, relative brain, kidney, and liver weights were significantly increased at 75 and 150 mg/kg. There were also differences in spleen, adrenal, and testes weights (absolute and/or relative). In females, absolute and/or relative kidney and liver weights were significantly increased at 150 mg/kg (liver) and at 75 and 150 mg/kg (kidney). There were no apparent treatment-related effects pertaining to mortality, ophthalmology, gross pathology, or histopathology.

Carcinogenic evaluation of 2,3-dimethyl-2,3-dinitrobutane via the mouse skin bioassay

Female SENCAR mice initiated with 2,3-dimethyl-2,3-dinitrobutane (DMDNB) and promoted with 12-O-tetradecanoylphorol-13-acetate (TPA) via the SENCAR mouse skin bioassay did not exhibit a significant increase in skin tumors. The mice received 20 mg kg-1 DMDNB divided into six intragastric doses over 2 weeks and were promoted three times per week for 20 weeks.

Ten and ninety-day toxicity studies of chloropicrin in Sprague-Dawley rats

The toxicity of chloropicrin (CP) was assessed following its administration to rats via oral gavage for either 10 or 90 consecutive days at dose levels of 10, 20, 40, and 80 mg/kg and 2, 8 and 32 mg/kg, respectively. Control rats received corn oil at a dose of 1.0 ml/kg. Toxicological observations included organ and body weight measurements, necropsy and histopathology observations, urinalysis, clinical chemistry and hematology determinations. The most remarkable toxicological finding in both studies was the corrosive property of CP on forestomach tissue. Inflammation, necrosis, acantholysis, hyperkeratosis and epithelial hyperplasia of the forestomach were seen in all dose groups of the 10-day study. Similar changes were detected in only the high dose group in the 90-day study. Decreased red blood cell parameters were noted in the highest dose groups in both studies, possibly due to blood loss via the damaged stomach lining. CP may have been aspirated into the lungs of animals in the high dose group in the ninety day study resulting in pulmonary complications leading to the deaths of 60% of the males and 80% of the females starting at week five. The 8 mg/kg dose group in the ninety day study was considered to be the no observed adverse effect level.

Toxicity of 1,1,1-trichloro-2-propanone in Sprague-Dawley rats

1,1,1-Trichloro-2-propanone (1,1,1-TCP) has been identified as a chlorination by-product in finished drinking water supplies. Since little was known of its oral toxicity, exposure studies were conducted with male and female Sprague-Dawley rats (10 males and 10 females/group) exposed by corn oil gavage at 0, 16, 48, 161, or 483 mg/kg for 10 d or 0, 30, 90, or 270 mg/kg for 90 d. Evaluations included mortality, clinical signs, body weight, food consumption, ophthalmology, hematology, clinical chemistry, urinalysis, organ weights, gross pathology, and histopathology. In the 10-d study, severe toxicity was observed at the highest dose level, since most treated animals (8/10 males and 7/10 females) died. Toxicity was also noted at 161 and 48 mg/kg. At 161 mg/kg, 2 males died and an increase in liver weights in both sexes was observed. Acanthosis and hyperkeratosis of the forestomach was present in males and females at 48 mg/kg and above. In the 90-d study, toxicity was significant at 270 mg/kg, with acanthosis and hyperkeratosis of the forestomach evident in most animals and ataxia in about one-half of them. Retinal degeneration, increased serum potassium, and increased blood urea nitrogen were present in females and increased blood calcium in males at that same dose level. Acanthosis and hyperkeratosis were observed in both sexes, and retinal degeneration was prominent in 2 females at 90 mg/kg. It was concluded that 16 mg/kg was the NOAEL (no observed adverse effect level) for the 10-d study while 30 mg/kg was the NOAEL for the 90-d exposure of Sprague-Dawley rats to 1,1,1,-trichloro-2-propanone.

Ten and ninety-day toxicity studies of 2,4-dimethylphenol in Sprague-Dawley rats

Male and female Sprague-Dawley rats received 2,4-dimethylphenol daily by gavage for 10 or 90 consecutive days. The 10-day acute study doses were 0, 60, 120, 600 and 1200 mg/kg; the 90-day subchronic study doses were 0, 60, 180 and 540 mg/kg. Corn oil was used as the vehicle. In the 10-day study, all the high dose animals died. At 600 mg/kg there was a significant increase in relative liver weight in females and several significant alterations in hematologic and clinical chemistry values in both sexes. Histopathological examination revealed changes associated with the forestomach in all dose groups. The 90-day study had numerous compound-related deaths at the 540 mg/kg level. In addition, the final body weight in high dose males and females was significantly less while absolute lung weights and relative liver weights in females, and relative brain, kidney and testes weights in males were also altered. Significant clinical chemistry findings in high dose animals (540 mg/kg) included reduced creatinine and increased cholesterol in both sexes, with increased triglycerides and decreased AST in males only. Histopathologic evaluation revealed hyperkeratosis and epithelial hyperplasia of the forestomach in males and females in the middle and high-dose groups.

Subchronic toxicity study of 1,3-dichloropropanone in Sprague-Dawley rats

1,3-Dichloropropanone (1,3-DCP) has been identified as a by-product of the chlorination of water and thus a potential contaminant in drinking water. Since little was known of its oral toxicity, subchronic exposure studies were conducted with male and female Sprague-Dawley rats exposed to 1,3-DCP in drinking water at 0, 5, 65, or 125 ppm for 90 days. Evaluations included mortality, clinical signs, body weight, food consumption, hematology, clinical chemistry, organ weights, gross pathology, and histopathology. No significant organ toxicity was detected although an aversion to drinking 1,3-DCP treated water was observed at 65 and 125 ppm. The only consistent change was a decrease in BUN at 125 ppm in both sexes. Based on a decrease in BUN levels and decreased water consumption, 5 ppm (0.5 mg/kg/day) was considered the NOAEL.

Ten and ninety-day toxicity studies of 2-chlorophenol in Sprague-Dawley rats

Male and female Sprague-Dawley rats received 2-chlorophenol in corn oil daily by gavage for 10 or 90 consecutive days. The 10-day study doses were 13, 64, 129 and 257 mg/kg while the 90-day subchronic study doses were 17, 50 and 150 mg/kg. In the 10-day study, hematologic and clinical chemistry, food and water consumption, absolute and relative organ weights, and histopathological findings revealed no compound or sex-related effects. In the 90-day study there were no significant gross or histopathological findings that were treatment-related in either sex. There were statistically significant differences between control and treated groups associated with hematology, clinical chemistry and organ weights; however, none of the differences were considered to be biologically meaningful.

Subchronic toxicity study of 1,1-dichloro-2-propanone in Sprague-Dawley rats

Groups of 10 male and 10 female Sprague-Dawley rats were administered 1,1-dichloro-2-propanone in corn oil by gavage at 0, 10, 20, 40, or 80 mg/kg/day for 90 consecutive days. Food and water consumption, body and organ weights, organ-to-body weight ratios, hematology, and clinical chemistry parameters were determined. Gross and microscopic pathology examinations also were conducted. No treatment-related mortality was observed during the study; however, liver, forestomach, and kidney toxicity was evident. Liver changes consisted of cytoplasmic alteration, cytomegaly, karyomegaly, and bile duct hyperplasia. These occurred with significance of p < or = 0.05 at or above 10 mg/kg/day in both sexes. The forestomach lesions included hyperkeratosis and epithelial hyperplasia in both sexes at 40 and 80 mg/kg/day, and ulcerations at 80 mg/kg/day. Also, an increased incidence and severity of spontaneously occurring chronic progressive nephropathy was most apparent in high dose males. Increases in organ-to-body weight ratios were noted for the liver and kidneys in females at the highest dose level and in males at the two highest dose levels. Serum enzymes (ALT, AST, and LDH) were increased in females and decreased in males. Based on liver lesions and biochemical changes, it was concluded that there was no experimentally definable NOAEL.

Chloroform inhibits the development of diethylnitrosamine-initiated, phenobarbital-promoted gamma-glutamyltranspeptidase and placental form glutathione S-transferase-positive foci in rat liver

In this study we demonstrate that chloroform, a widely used industrial solvent, a medicinal chemical and a common drinking water contaminant, reduces the number of detectable preneoplastic enzyme-altered foci [gamma-glutamyltranspeptidase-positive (GGT+) and placental form glutathione S-transferase-positive (GST-P+)] in the liver of male Fischer 344 rats. The animals were given a partial hepatectomy and 18 h later received a single oral dose of either 0.5 mmol/kg diethylnitrosamine (DENA) or saline. Two weeks later, groups of 12 animals were started on drinking water containing phenobarbital with varying concentrations (200-1800 mg/l) of chloroform fro 12 weeks. Treated and control animals were killed and the number and the volume of GGT+ and GST-P+ expressing hepatic foci were tabulated. The numbers of foci per unit volume (and per unit area), the percent focal volume and the focal liver were reduced by chloroform in a dose-dependent manner. The mean focal volume was not influenced by chloroform. A plausible explanation for these results could be that chloroform exerts its focal inhibitory effect either by selectively killing the putative initiated cells, by retarding the inherent growth rate of enzyme-altered cells or by reducing the effectiveness of the promoter, phenobarbital. The available evidence suggests that the first hypothesis is the most likely explanation for these observations. These results are consistent with earlier studies showing that chloroform inhibits tumorigenesis in rodents.

Hepatocarcinogenicity of chloral hydrate, 2-chloroacetaldehyde, and dichloroacetic acid in the male B6C3F1 mouse

The chlorinated acetaldehydes, chloral hydrate (CH) and 2-chloroacetaldehyde (CAA), have been identified as chlorination by-products in finished drinking water supplies. Although both chemicals are genotoxic, their potential for carcinogenicity had not been adequately explored. The studies reported here are chronic bioassays conducted with male B6C3F1 mice exposed to levels of 1 g/liter CH and 0.1 g/liter CAA via the drinking water for 104 weeks. Distilled water (H2O) served as the untreated control and dichloroacetic acid (DCA; 0.5 g/liter), another chlorine disinfection by-product, was included. The mean daily ingested doses were approximately 166 mg/kg/day for CH, 17 mg/kg/day for CAA, and 93 mg/kg/day for DCA. Evaluations included mortality, body weight, organ weights, gross pathology, and histopathology. The primary target organ was the liver as the organ weights and pathological changes in the other organs (spleen, kidneys, and testes) were comparable between the treated groups and the H2O control group. Liver weights were increased for all three test chemicals at the terminal euthanasia with the greatest increase seen in the CH and DCA groups. Hepatocellular necrosis was induced by all three test chemicals, and it was also most prevalent and severe in the CH and DCA groups. A significant increase in the prevalence of liver tumors was seen for all three chemicals. The strongest response was with DCA, in which 63% of the 104-week survivors had hepatocellular carcinomas (carcinomas) and 42% possessed hepatocellular adenomas (adenomas) and the combined prevalence for carcinomas plus adenoma was 75%. The corresponding prevalence rate for carcinomas, adenomas, and combined tumors were 46, 29, and 71%; 31, 8, and 38%; and 10, 5, and 15% for CH, CAA, and H2O, respectively. In addition to the tumors we evaluated the prevalence of a possible preneoplastic lesion, the hepatocellular hyperplastic nodule (nodules), a lesion which occurred in all three treated groups but not in the H2O group.

Ninety-day toxicity study of chloral hydrate in the Sprague-Dawley rat

Male and female Sprague-Dawley rats were administered drinking water containing 300, 600, 1200, or 2400 mg/L chloral hydrate for 90 days. A control group received distilled water only. No animals died during the study and no differences were observed in body weight gain or food and water consumption, except for males at the highest-dose level. Minor treatment-related effects were observed for organ weights and hematological parameters and these did not appear to be of toxicological significance. Some indications of toxicity were evident in the 2400 mg/L male group (equivalent to 168 mg/kg-day) including a significant decrease in food and water consumption and in weight gain. In addition, histopathological examination of these animals revealed an apparent increase in the incidence of focal hepatocellular necrosis. Increases in AST, ALT, and LDH, which occurred at several dose levels in males, but particularly at 200 mg/L, are consistent with the hepatocellular necrosis of minimal to mild severity diagnosed by microscopic examination. These liver changes, except for sporadic enzyme changes, were not seen in the female rats which actually consumed higher doses of chloral hydrate (e.g., 288 mg/kg-day at 2400 mg/L). On the basis of the mild liver toxicity (histopathological and clinical) observed in males at the highest doses (168 mg/kg-day), the no observed adverse effect level (NOAEL) for oral exposure of rats to chloral hydrate for 90 days is considered to be 96 mg/kg-day (600 mg/L).

90-Day toxicity study of dichloroacetate in dogs

Male and female juvenile beagle dogs were dosed daily for 90 days with dichloroacetate (DCA). The compound was administered orally via gelatin capsules at doses of 0, 12.5, 39.5, and 72 mg/kg/day. Each dose group consisted of five males and five females. The dogs were observed clinically and blood samples were taken at 15-day intervals for hematologic and serum chemistry values. Decreased total erythrocyte count and hemoglobin levels were observed in mid- and high-dose dogs beginning at Day 30. Serum concentrations of LDH were elevated at Days 30 and 45 in females and at Day 75 in males treated with DCA at 72 mg/kg/day. One female of the high-dose group died at Day 50 and two high-dose males died at Days 51 and 74. Hindlimb partial paralysis was observed in many high-dose dogs. Vacuolization of myelinated white tracts of cerebrum, cerebellum, and/or spinal cord was observed in many high-dose dogs as well as some mid- and low-dose subjects. Degeneration of testicular germinal epithelium and syncytial giant cell formation was noted in males of all dose groups. Hepatic vacuolar change and chronic hepatitis appeared only in DCA-treated dogs. In addition, suppurative bronchopneumonia and chronic pancreatitis were noted in many high-dose and some middose subjects. A "no-adverse-effect level" was not determined in this study.

Ninety-day toxicity study of sodium monochloroacetate in Sprague-Dawley rats

Male and female Sprague-Dawley rats were administered the sodium salt of monochloroacetic acid (SMCA) by oral gavage for a period of 90 consecutive days. Dosage levels of 15, 30, 60 or 120 mg/kg per day were employed. SMCA clearly induced toxicity in both females and males, with the greatest severity in the male animals. Both the liver and kidneys were identified as target organs. At 120 mg/kg per day, 30% of females and 80% of the males died, most within the first 2 days of treatment. Hemorrhagic and congested lungs (possibly a postmortem change) were seen in the early deaths (1-3 days) whereas liver lesions were observed in later deaths. In addition, there was nephrotoxicity as evidenced by elevated creatinine, blood calcium (BCAL), and blood urea nitrogen (BUN) levels. Hepatotoxicity was indicated by increases in the serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Both organs showed increased organ-to-body weight ratios. Microscopic examination revealed a significant (P less than or equal to 0.001) increase in chronic renal nephropathy and increased splenic pigmentation at 60 mg/kg per day in the males. Based on the observation of toxicity at all treatment levels in males, a lowest observed adverse effect level (LOAEL) of 15 mg/kg per day is proposed for a 90-day exposure to SMCA by oral gavage to the Sprague--Dawley rat.

Site-specific modulation of carcinogen-induced gastrointestinal tract nuclear anomalies in B6C3F1 mice by chloroform

Chloroform (CHCl3) is an established rodent carcinogen and a prevalent contaminant of chlorine-disinfected drinking water. Thus in the United States CHCl3, along with other trihalomethanes, is regulated not to exceed 100 ppb in potable water. Recently, several studies have shown that CHCl3 also has anti-cancer properties as it inhibits tumor growth in mouse liver and in the gastrointestinal tract of the rat. In this paper we show that CHCl3 also inhibits the propensity for three gastrointestinal tract carcinogens, benzo(a)pyrene (BAP), 1,2-dimethylhydrazine (DMH) and methylnitrosourea (MNU), to induce nuclear anomalies in the proximal colon of the B6C3F1 mouse. For example, in mice pre-adapted to 1800 ppm CHCl3 for 30 days prior to the carcinogen administration the level of nuclear anomalies induced in the proximal colon by BAP was reduced by four-fold (0.9 +/- 0.7 v. 3.6 +/- 1.0 anomalies/10 crypts; p less than 0.001) and two-fold for MNU (2.4 +/- 1.0 v. 4.6 +/- 1.6; p less than 0.001) and DMH (0.9 +/- 0.9 v. 1.7 +/- 0.8; p = 0.03). In the duodenum CHCl3 was effective at inhibiting unclear anomalies only for MNU (45.3 +/- 4.6 v. 30.4 +/- 3.5; p = 0.02). The inhibitory effect of CHCl3 does not extend to nuclear anomalies of the forestomach. The anti-cancer properties of CHCl3 are discussed in light of its cancer causing potential and possible application to human risk assessment.