Toxicology and carcinogenicity studies of diuretics in F344 rats and B6C3F1 mice. 2. Furosemide

Toxicology and carcinogenesis studies of furosemide, a widely used diuretic, were conducted by administering diets containing the drug to both sexes of F344 rats and B6C3F1 mice in 14-day, 13-week and 2-year studies. Deaths occurred among rats and mice receiving diets containing 46,000 ppm furosemide in 14-day studies, and animals given diets containing lower concentrations lost weight. No deaths were seen in 13-week studies using top concentrations ranging from 10,000 to 20,000 ppm, but animals at higher concentrations had lower weight gains than controls. Nephrosis in rats and mice was the only significant compound-related lesion observed in the prechronic studies. In 2-year studies, rats received diets containing 0, 350 or 700 ppm furosemide and mice received diets containing 0, 700 or 1400 ppm furosemide. Survival of dosed and control rats of both sexes and male mice was similar; survival of high-dose female mice was lower than controls. Nephropathy was increased in male rats and in male and female mice. In female mice, increased malignant tumors of the mammary gland were associated with furosemide administration. In male rats, marginal increases in tubular cell neoplasms of the kidney and in meningiomas of the brain were observed in dosed animals, but these were not considered to be related clearly to exposure to furosemide.

No evidence of toxicity or carcinogenicity of pentaerythritol tetranitrate given in the diet to F344 rats and B6C3F1 mice for up to two years

Toxicology and carcinogenesis studies of pentaerythritol tetranitrate (PETN), an organic nitrate used in explosives and as a therapeutic agent for angina pectoris, were conducted by administering diets containing PETN,NF (National Formulary Grade, a 1:4 mixture of PETN and lactose) to both sexes of F344 rats and B6C3F1 mice in 14-day, 13-week and 2-year studies. PETN was found to be essentially non-toxic in 14-day and 13-week studies at dietary concentrations as high as 10,000 ppm; the weight gain of female rats was lower than that of controls at 5000 and 10,000 ppm in the 13-week study. In the 13-week studies, one in ten high-dose female rats had an adenoma of the Zymbal gland and one in ten high-dose female mice had a hepatocellular adenoma. Dietary concentrations chosen for the 2-year studies were 5000 and 10,000 ppm for male rats and male and female mice, and 1240 and 2500 ppm for female rats. In the 2-year studies, there were no adverse effects on survival or body weight gains in either sex of rats or mice. No neoplastic or non-neoplastic lesions were considered to be related clearly to PETN administration. Neoplasms of the Zymbal gland occurred at low incidences in PETN-exposed groups of both sexes of rats in the 2-year study.

Use of statistical decision rules for evaluating laboratory animal carcinogenicity studies

In the evaluation of long-term rodent carcinogenicity studies, many different tumor sites and types are evaluated, which may increase the likelihood of a statistical false positive. To deal with this issue, a number of statistical decision rules have been proposed that take into account multiple comparisons. This paper discusses the various types of decision rules and evaluates the factors that may lead to different interpretations of experimental results. These concepts are illustrated by examining the statistical decision procedures used by three analysts to evaluate the results of 25 long-term rodent carcinogenicity studies carried out by the National Cancer Institute. Agreement among these decision rules is shown to be greater than originally reported. It is also concluded that while the application of statistical decision rules may be of value in some instances to guard against statistical false positives, the final interpretation of the data should be based on biological as well as statistical considerations. Thus, statistical decision rules should not be employed as a substitute for sound scientific judgment in the overall evaluation of these experiments.

Growth, body weight, survival, and tumor trends in F344/N rats during an eleven-year period

Time trends for growth, body weight, survival and tumor prevalences in 144 diet control groups with a total of 5,184 male F344/N rats and 146 diet control groups with a total of 5,289 female rats of NCI-NTP 2-yr chemical carcinogenicity studies started during an 11-yr period (1971 to 1981) in 11 toxicology testing laboratories were evaluated. Male and female rats in more recent studies grew faster and attained a higher body weight than rats from earlier studies. Survival of males showed a significantly decreasing trend over time, which may have been related to diseases associated with increasing body weight, prevalence of leukemia and changes in criteria for euthanasia of moribund animals. The time trend for survival of females was not significant. There were highly significant (p less than 0.001) positive time trends for prevalences of leukemia, anterior pituitary tumors and thyroid C-cell tumors in both sexes, adrenal pheochromocytomas in males and mammary tumors and endometrial stromal polyps in females. The prevalence of mammary tumors in females and pituitary tumors in males had a highly significant (p less than 0.01) positive association with body weight. Histological reevaluation of tumor prevalences in approximately 250 rats of each sex at each of 4 different time periods indicated that changes in diagnostic criteria may have contributed to but could not totally explain the increased prevalence of leukemia. Changes in diagnostic criteria and the amount of tissue examined may have contributed to the increased prevalence of anterior pituitary tumors in both sexes and adrenal pheochromocytomas in males. Interlaboratory variability and changes in diet may also have contributed to the time-related trends.

Growth, body weight, survival, and tumor trends in (C57BL/6 X C3H/HeN) F1 (B6C3F1) mice during a nine-year period

Time trends for growth, body weight, survival and tumor prevalences in 121 diet control groups with a total of 4,636 male B6C3F1 mice and 123 diet control groups with a total of 4,758 female mice of NCI-NTP 2-yr chemical carcinogenicity studies started during a 9-yr period (1973 to 1981) in 11 laboratories were evaluated. Male and female mice did not show substantial changes in growth patterns. Both sexes had highly significant time trends with decreasing body weights in the more recent studies. This apparent trend was due to high body weights during the first 3 yr and highly significant interlaboratory variability. Time trends for survival of both sexes were not significant. Prevalences of liver tumors, lung tumors, and lymphoma in males and lung tumors in females did not show significant time trends. There were significant positive time trends for prevalences of liver tumors and lymphoma in female mice, but the trends were not significant when adjusted for interlaboratory variability. The positive time trend for anterior pituitary tumors of females was highly significant and may be due in part to an increase in the amount of pituitary tissue examined in the more recent studies. Histological reevaluation of liver and anterior pituitary tissue in 208-249 female mice at each of 4 different times periods did not substantially change the prevalences or the time trends. The major factor influencing time trends in mice appeared to be interlaboratory variability.

Influence of viral infections on body weight, survival, and tumor prevalence in Fischer 344/NCr rats on two-year studies

Sendai virus (SV), pneumonia virus of mice (PVM), and rat coronavirus/sialodacryoadenitis virus (RCV/SDAV) were common viral infections of rats in the National Cancer Institute-National Toxicology Program (NCI-NTP) studies from 1977 to 1983. Influence of these viral infections on body weight, survival, and prevalences of spontaneous tumors in the F344/NCr rats of 28 diet control groups at five different laboratories were evaluated. Tumor prevalences evaluated in this investigation included the following: leukemia and tumors of the anterior pituitary, lungs, salivary glands and Harderian glands in both sexes; adrenal pheochromocytomas in male rats; and mammary tumors in female rats. SV and PVM but not RCV/SDAV infections were associated with significant (P less than 0.05) decreases in body weights of male and female rats. Male rat groups with PVM infection had a lower prevalence of leukemia and male rat groups with RCV/SDAV infection had a higher prevalence of anterior pituitary tumors than the corresponding uninfected groups. Female rat groups with SV infection had greater survival and a higher prevalence of lung tumors than groups without SV infection. However, none of the tumor prevalence and survival differences were statistically significant when interlaboratory variability and time-related effects were taken into account.

Influence of viral infections on body weight, survival, and tumor prevalence of B6C3F1 (C57BL/6N x C3H/HeN) mice in carcinogenicity studies

Sendai virus (SV), mouse hepatitis virus (MHV), and pneumonia virus of mice (PVM) are common viral infections of mice. Influence of these viral infections on the prevalence of liver tumors, lung tumors, and lymphoma is of concern in chemical carcinogenicity studies. Body weight, survival, and tumor prevalence of B6C3F1 mice with and without viral infections in 33 male and 34 female untreated control groups and 32 male and 32 female low- and high-dose groups of 2-year chemical carcinogenicity studies were evaluated. In male mice, the SV infection was associated with significantly (p less than 0.05) higher survival of control, low-dose, and high-dose groups, and higher prevalence of liver tumors and lymphoma. The increases in tumor prevalence are possibly due to an increase in the survival of male mice that had SV infection. However, when interlaboratory variability and time-related effects were taken into account, the number of significant effects was consistent with the expected false-positive rate inherent to the statistical procedures. The MHV and PVM infections did not cause consistent changes in body weight, survival, and tumor prevalences in the control and chemical treatment groups of male mice. Viral infections did not cause consistent increases or decreases in body weight, survival, or tumor prevalence in the control and chemical treatment groups of female B6C3F1 mice.

Multiple-site carcinogenicity of benzene in Fischer 344 rats and B6C3F1 mice

Toxicology and carcinogenesis studies of benzene (CAS No. 71-43-2; greater than 99.7% pure) were conducted in groups of 60 F344/N rats and 60 B6C3F1 mice of each sex for each of three exposure doses and vehicle controls. These composite studies on benzene were designed and conducted because of large production volume and widespread human exposure, because of the epidemiologic association with leukemia, and because previous experiments were considered inadequate or inconclusive for determining carcinogenicity in laboratory animals. Using the results from 17-week studies, doses for the 2-year studies were selected based on clinical observations (tremors in higher dosed mice), on clinical pathologic findings (lymphoid depletion in rats and leukopenia in mice), and on body weight effects. Doses of 0, 50, 100, or 200 mg/kg body weight benzene in corn oil were administered by gavage to male rats, 5 days per week, for 103 weeks. Doses of 0, 25, 50, or 100 mg/kg benzene in corn oil were administered by gavage to female rats and to male and female mice for 103 weeks. Ten animals in each of the 16 groups were killed at 12 months, and necropsies were performed. Hematologic profiles were performed at 3-month intervals. For the 2-year studies, mean body weights of the top dose groups of male rats and of both sexes of mice were lower than those of the controls. Survivals of the top dose group of rats and mice of each sex were reduced; however, at week 92 for rats and week 91 for mice, survival was greater than 60% in all groups; most of the dosed animals that died before week 103 had neoplasia. Compound-related nonneoplastic or neoplastic effects on the hematopoietic system, Zymbal gland, forestomach, and adrenal gland were found both for rats and mice. Further, the oral cavity was affected in rats, and the lung, liver, Harderian gland, preputial gland, ovary, and mammary gland were affected in mice. Under the conditions of these 2-year gavage studies, there was clear evidence of carcinogenicity of benzene in male F344/N rats, female F344/N rats, male B6C3F1 mice, and female B6C3F1 mice. In male rats, benzene caused increased incidences of Zymbal gland carcinomas, squamous cell papillomas and squamous cell carcinomas of the oral cavity, and squamous cell papillomas and squamous cell carcinomas of the skin. In female rats, benzene caused increased incidences of Zymbal gland carcinomas and squamous cell papillomas and squamous cell carcinomas of the oral cavity.(ABSTRACT TRUNCATED AT 400 WORDS)

Occurrence and relevance of chemically induced benign neoplasms in long-term carcinogenicity studies

Recent carcinogenicity studies conducted and evaluated by the National Toxicology Program/National Institute of Environmental Health Sciences were examined to determine the frequency of chemically increased incidences of neoplasia. Many of the chemicals originally selected for study were chosen because of an a priori suggestion that they might be carcinogens. Of the 143 chemical studies evaluated, usually involving male and female rats and mice, 42 (29%) did not induce any neoplasms, 20 (14%) gave marginal or equivocal neoplastic responses, and 81 (57%) showed positive neoplastic responses in one or more of the 524 species-gender experiments. Of these 81 positive studies, 60 (74%) were considered positive based on malignant neoplasia, 16 (20%) were positive due primarily to benign neoplasia, but had supporting evidence of malignant neoplasia in the same organ/tissue, and 5 (6%) were positive based only on benign neoplasia. These five chemicals are a) allyl isothiocyanate (transitional cell papillomas of the urinary bladder in male rats), b) 2-amino-4-nitrophenol (tubular cell adenomas of the kidney in male rats), c) asbestos intermediate range chrysotile (adenomatous polyps of the large intestine in male rats), d) decabromodiphenyl oxide (neoplastic nodules of the liver in male and female rats), and e) nitrofurazone (fibroadenomas of the mammary gland in female rats and benign mixed tumors and granulosa cell tumors of the ovary in female mice). For all but one of these lesions (mammary gland), the occurrence in historic controls is low. Thus, only 5 of the 143 chemicals studied (3.5%) induced benign neoplasia alone, and those observed benign neoplasms are known to progress to malignancy. Accordingly, we consider chemically induced benign neoplasia to be an important indicator of a chemical's carcinogenic potential in rodents, and believe it should continue to be made an integral part of the overall weight-of-the-evidence evaluation process for identifying potential human health hazards.

Sources of variability in rodent carcinogenicity studies

A number of factors may influence tumor rates in rodent carcinogenicity studies, including the animal room environment, genetic differences, food consumption/weight gain, survival/age of the animals, identification of gross lesions, pathology sampling procedures and preparation of the histology slides, and histopathologic diagnosis. The relative importance of these factors is evaluated, making use of laboratory animal carcinogenicity data from the National Toxicology Program and from other sources. An investigator must be aware of these potentially confounding factors, so that appropriate measures can be taken to reduce or eliminate their impact on the interpretation of study results. Certain potential sources of within-study variability can be controlled by appropriate experimental design and by proper conduct according to standard operating procedures. The effect of certain factors influencing tumor prevalence may be magnified when variability from study to study is considered, and thus it may be difficult to formulate a biologically meaningful statistical analysis that uses historical control data in a formal testing framework.

Two-year toxicity and carcinogenicity studies of ampicillin trihydrate and penicillin VK in rodents

Toxicology and carcinogenesis studies of ampicillin trihydrate and penicillin VK, two widely used beta-lactam antibiotics, were performed in F344/N rats and B6C3F1 mice. In these studies ampicillin trihydrate was administered for 2 years to rats at doses of 0, 750, or 1500 mg/kg and to mice at doses of 0, 1500, or 3000 mg/kg, and penicillin VK was administered to rats and mice at doses of 0, 500, or 1000 mg/kg. Both drugs were administered by oral gavage in corn oil. Toxic lesions of the stomach were seen in rats and mice after ampicillin trihydrate administration and in mice after penicillin VK administration. In male rats that received ampicillin trihydrate there was a marginal increase in incidence of mononuclear cell leukemia and pheochromocytomas of the adrenal gland medulla. There was no evidence for carcinogenic activity in female rats or male and female mice after ampicillin trihydrate administration or in rats and mice after penicillin VK administration.

Toxicity and carcinogenicity of nitrofurazone in F344/N rats and B6C3F1 mice

Toxicology and carcinogenesis studies were conducted by feeding diets containing nitrofurazone (99% pure) to groups of F344/N rats and B6C3F1 mice for 14 days, 13 wk or 2 yr. In the 14-day studies, in which doses ranged from 630 to 10,000 ppm, nitrofurazone was more toxic to mice than to rats. Accordingly, in the 13-wk studies, doses for rats ranged from 150 to 2500 ppm and for mice from 70 to 1250 ppm. At the higher doses, convulsive seizures and gonadal hypoplasia were observed in both species. Evidence of toxicity in rats also included degenerative arthropathy. For the 2-yr studies, rats were exposed to 0, 310 or 620 ppm nitrofurazone and the survival of male rats given 620 ppm was lower than that of controls (33/50, 30/50 and 20/50 in the control, 310- and 620-ppm groups, respectively). Nitrofurazone administration increased the incidences of mammary gland fibroadenomas in female rats (8/49, 36/50 and 36/50 in the control, 310- and 620-ppm groups, respectively). In male rats it was associated with a marginal increase in sebaceous gland adenomas and trichoepitheliomas of the skin, mesotheliomas of the tunica vaginalis, and tumours of the perputial gland. Nitrofurazone caused testicular degeneration (atrophy of germinal epithelium and aspermatogenesis) in rats, and degeneration of vertebral and knee articular cartilage in rats of both sexes. In mice, dietary concentrations of nitrofurazone for the 2-yr studies were 0, 150 or 310 ppm. In mice of each sex, nitrofurazone administration induced stimulus-sensitive convulsive seizures, primarily during the first year of study. In male mice, there was no evidence of any chemically-related carcinogenic effects, but there was a treatment-related decrease in survival (39/50, 31/50 and 27/50 in the control, 150- and 310-ppm groups, respectively). In female mice nitrofurazone induced ovarian lesions with increased incidences of benign mixed tumours (0/47, 17/50 and 20/50 in control, low- and high-dose groups, respectively) and granulosa cell tumours (1/47, 4/50 and 9/50 in control, low- and high-dose groups, respectively).

Sources of Variability in Rodent Carcinogenicity Studies

Sources of Variability in Rodent Carcinogenicity Studies. HASEMAN, J. E., HUFF, J. E., RAO, G. K, AND EUSTIS, S. L. (1989). Fundam. Appl Toxicol. 12, 793–804. A number of factors may influence tumor rates in rodent carcinogenicity studies, including the animal room environment, genetic differences, food consumption/weight gain, survival/age of the animals, identification of gross lesions, pathology sampling procedures and preparation of the histology slides, and histopathologic diagnosis The relative importance of these factors is evaluated, making use of laboratory animal carcinogenicity data from the National Toxicology Program and from other sources. An investigator must be aware of these potentially confounding factors, so that appropriate measures can be taken to reduce or eliminate their impact on the interpretation of study results. Certain potential sources of within-study variability can be controlled by appropriate experimental design and by proper conduct according to standard operating procedures. The effect of certain factor influencing tumor prevalence may be magnified when variability from study to study is considered, and thus it may be difficult to formulate a biologically meaningful statistical analysis that uses historical control data in a formal testing framework.

Two-year inhalation carcinogenesis studies of methyl methacrylate in rats and mice: inflammation and degeneration of nasal epithelium

Methyl methacrylate (MMA), a liquid monomer, is used as a chemical intermediate in the manufacture of plexiglass and other acrylic products and as "bone cement" in orthopedic and dental surgery. Toxicology and carcinogenesis inhalation studies of MMA were conducted because of: (1) widespread human exposure; (2) evidence of mutagenicity; and (3) inadequacy of previously conducted long-term oral, dermal, and inhalation studies. Groups of 50 male F344/N rats were exposed to MMA by inhalation at 0, 500, or 1000 ppm, female F344/N rats at 0, 250, or 500 ppm, and male and female B6C3F1 mice at 0, 500, or 1000 ppm, 6 h a day, 5 days a week for 102 weeks. Survival rates of male and female rats and mice exposed to MMA were similar to those of their respective controls. Body weights were reduced in the low and high dose male (3-6% and 5-10%, respectively) and female (5-7% and 8-10%) rats exposed to MMA for more than 80 weeks and in male (7-19% and 6-17%) and female (0-13% and 0-17%) mice for more than 20 weeks. Inhalation exposure of MMA for 102 weeks did not induce any increased incidences of neoplasms in male or female rats or mice. Non-neoplastic lesions in the nasal cavity of MMA-exposed rats and mice were significantly increased and these included inflammation and degeneration of the olfactory epithelium of MMA-exposed male and female rats and inflammation, hyperplasia, cytoplasmic inclusions in the respiratory epithelium, and degeneration of the olfactory epithelium in male and female mice.

The impact of toxicity on carcinogenicity studies: implications for risk assessment

This paper explores the inter-relationship between toxicity, genotoxicity, and carcinogenicity in laboratory rodents. To our knowledge this is the first attempt to integrate these factors and evaluate their implications for the process of risk assessment. The evaluation is based on information obtained from 2-year laboratory-animal studies involving 99 chemicals. The data suggest that only seven of the 53 positive carcinogenicity studies exhibited the types of target organ toxicity that could have been the cause of all observed carcinogenic effects. Furthermore, no apparent difference in mutagenicity as measured by the Ames Salmonella assay was observed between 'high dose only' carcinogens and the entire set of carcinogens. These findings suggest that the number of chemical carcinogens that we can identify solely through rodent studies as being potential tumor inducers through some indirect mechanism is small. Generally speaking, the identification of histopathological effects is not sufficient in itself for justifying mechanistic assumptions, and supplemental biological information will be necessary to reach definitive conclusions.

Do cage effects influence tumor incidence? An examination of laboratory animal carcinogenicity studies utilizing Fischer 344 rats

Approximately 125 carcinogenicity studies in Fischer 344 rats conducted by the National Toxicology Program (NTP) were examined to determine the frequency with which cage effects were associated with observed carcinogenic responses. All studies involving groups of 50 rats housed five per cage and showing evidence of chemically-related carcinogenicity were considered. For each of these experiments, two statistical analyses were carried out for each dosed and control group: (i) a test to determine whether or not the occurrence of tumors clustered within cages; and (ii) an evaluation to determine whether or not tumor incidences differed significantly between differing cage shelf levels. These analyses showed that the numbers of statistically significant (P less than 0.05 or P less than 0.01) effects were consistent with the number expected by chance alone. Thus, cage-related factors appeared to have little or no impact upon tumor incidence in these particular studies. Experimental design protocols now used by the NTP (which include random assignment of animals to cages; random assignment of columns of cages to dosed and control groups; and periodic rotation of cage location) further reduce the likelihood that factors associated with the housing of the animals could influence tumor incidence in current studies.

Development of kidney tumors in the male F344/N rat after treatment with dimethyl methylphosphonate

Dimethyl methylphosphonate (DMMP), a chemical that has been used as a flame retardant and as a nerve gas simulant to mimic the physical but not biologic properties of nerve gases, was administered by gavage in corn oil for up to 2 years at doses of 0, 500, or 1000 mg/kg/day to male and female F344/N rats and at doses of 0, 1000, or 2000 mg/kg/day to male and female B6C3F1 mice. Survival in dosed male rats was reduced, due in part to kidney toxicity, and lesions in the kidney included increased severity of spontaneous nephropathy, calcification, hyperplasia of the tubular and transitional epithelium, tubular cell adenocarcinomas, and transitional cell papillomas and carcinomas. Survival in female rats was similar among groups; survival in mice was reduced and this reduced survival decreased the sensitivity for detecting a carcinogenic response. There were no dose-related neoplastic responses in female rats or male or female mice. The spectrum of kidney lesions seen in the male rat given DMMP is similar to that seen after the long-term administration of a variety of other chemicals including unleaded gasoline, hydrocarbon solvents, and 1,4-dichlorobenzene.

Toxicity and carcinogenicity studies of phenylephrine hydrochloride in F344/N rats and B6C3F1 mice

Phenylephrine HCl was incorporated into feed given to male and female F344/N rats and B6C3F1 mice in studies of 14 days, 12 weeks, and 2 years duration. In 12-week studies, body weight gains decreased with dose, and deaths of male rats and mice occurred at concentrations of 5,000 ppm and above; however, no organ-specific toxicity was evident. During 2-year studies, body weights of rats receiving diets at 620 and 1,250 ppm and mice at 1,250 and 2,500 ppm ranged up to 16% less than control. Survival of high dose male rats was substantially greater than controls. Survivals of other dose groups of rats and mice were similar to controls. Chronic focal inflammation of the liver, and inflammation of the prostate were increased in dosed rats. No increases in neoplasms were observed in rats or mice consuming diets containing phenylephrine HCl for 2 years. The incidences of mononuclear cell leukemia and pheochromocytomas of the adrenal gland were decreased in dosed male rats. Approximate time weighted average doses ranged up to 54 mg/kg/day for rats and 280 mg/kg/day for mice during the 2-year studies.