Background data and variations in tumor rates of control rats and mice

Odours of cancerous mouse congeners: detection and attractiveness

Chemical communication plays a major role in social interactions. Cancer, by inducing changes in body odours, may alter interactions between individuals. In the framework of research targeting non-invasive methods to detect early stages of cancer development, this study asked whether untrained mice could detect odour changes in cancerous congeners. If yes, were they able to detect cancer at an early developmental stage? Did it influence female preference? Did variations in volatile organic components of the odour source paralleled mice behavioural responses? We used transgenic mice strains developing or not lung cancer upon antibiotic ingestion. We sampled soiled bedding of cancerous mice (CC) and not cancerous mice (NC), at three experimental conditions: before (T0), early stage (T2) and late stage (T12) of cancer development. Habituation/generalisation and two-way preference tests were performed where soiled beddings of CC and NC mice were presented to wild-derived mice. The composition and relative concentration of volatile organic components (VOC) in the two stimuli types were analysed. Females did not show directional preference at any of the experimental conditions, suggesting that cancer did not influence their choice behaviour. Males did not discriminate between CC and NC stimuli at T0 but did so at T2 and T12, indicating that wild-derived mice could detect cancer at an early stage of development. Finally, although the VOC bouquet differed between CC and NC it did not seem to parallel the observed behavioural response suggesting that other types of odorant components might be involved in behavioural discrimination between CC and NC mice.

Summary: Male mice could discriminate the smell of cancerous congeners even when the tumour was hardly detectable by other means; however, females did not discriminate against the smell of males carrying cancerous tumours. Odorant molecules other than volatile organic compounds analysed here might explain the observed behaviour.

The three dimensions of somatic evolution: Integrating the role of genetic damage, life-history traits, and aging in carcinogenesis

Tumors result from genetic and epigenetic alterations that change cellular survival and differentiation probabilities, promoting clonal dominance. Subsequent genetic and selection processes in tumors allow cells to lose their tissue fidelity and migrate to other parts of the body, turning tumors into cancer. However, the relationship between genetic damage and cancer is not linear, showing remarkable and sometimes seemingly counterintuitive patterns for different tissues and across animal taxa. In the present paper, we attempt to integrate our understanding of somatic evolution and cancer as a product of three major orthogonal processes: occurrence of somatic mutations, evolution of species-specific life-history traits, and physiological aging. Patterns of cancer risk have been shaped by selective pressures experienced by animal populations over millions of years, influencing and influenced by selection acting on traits ranging from mutation rate to reproductive strategies to longevity. We discuss how evolution of species shapes their cancer profiles alongside and in connection with other evolving life-history traits and how this process explains the patterns of cancer incidence we observe in humans and other animals.

From humans to hydra: patterns of cancer across the tree of life

Cancer is a disease of multicellularity; it originates when cells become dysregulated due to mutations and grow out of control, invading other tissues and provoking discomfort, disability, and eventually death. Human life expectancy has greatly increased in the last two centuries, and consequently so has the incidence of cancer. However, how cancer patterns in humans compare to those of other species remains largely unknown. In this review, we search for clues about cancer and its evolutionary underpinnings across the tree of life. We discuss data from a wide range of species, drawing comparisons with humans when adequate, and interpret our findings from an evolutionary perspective. We conclude that certain cancers are uniquely common in humans, such as lung, prostate, and testicular cancer; while others are common across many species. Lymphomas appear in almost every animal analysed, including in young animals, which may be related to pathogens imposing selection on the immune system. Cancers unique to humans may be due to our modern environment or may be evolutionary accidents: random events in the evolution of our species. Finally, we find that cancer‐resistant animals such as whales and mole‐rats have evolved cellular mechanisms that help them avoid neoplasia, and we argue that there are multiple natural routes to cancer resistance.

Rodent models for the preclinical evaluation of drugs suitable for pharmacological intervention in aging

INTRODUCTION

There is a growing scientific and public interest in the development of new antiaging drugs for the purposes of extending mean and/or maximum life span, maintaining normal physiological function, and alleviating the onset and severity of age-associated diseases. This review looks at the current screening approaches used to evaluate the efficacy of such compounds, with a particular focus on those that extend life span.

AREAS COVERED

This article reviews the current preclinical approaches for assessing longevity therapy including the assessment of antiaging drugs (aging reversal) and geroprotectors (drugs that prevent premature aging and/or slowdown or postpone aging). This article also discusses the methods and the importance in evaluating the anticarcinogenic potential and safety of antitumor drugs.

EXPERT OPINION

Based on more than 30 years of experience in the field, the authors believe that the standard testing protocols for antiaging drugs should include the simultaneous evaluation of the drug's safety, as well as its antitumor and anticarcinogenic activity potential. The authors also believe that the principles of international programs for the expert critical evaluation of pharmacological interventions should be created to improve the range of antiaging interventions available for human studies.

Aging-associated changes in hematopoiesis and leukemogenesis: what's the connection?

Aging is associated with a marked increase in a number of diseases, including many types of cancer. Due to the complex and multi-factorial nature of both aging and cancer, accurate deciphering of causative links between aging and cancer remains a major challenge. It is generally accepted that initiation and progression of cancers are driven by a process of clonal evolution. In principle, this somatic evolution should follow the same Darwinian logic as evolutionary processes in populations in nature: diverse heritable types arising as a result of mutations are subjected to selection, resulting in expansion of the fittest clones. However, prevalent paradigms focus primarily on mutational aspects in linking aging and cancer. In this review, we will argue that age-related changes in selective pressures are likely to be equally important. We will focus on aging-related changes in the hematopoietic system, where age-associated alterations are relatively well studied, and discuss the impact of these changes on the development of leukemias and other malignancies.

Relationships between cancer and aging: a multilevel approach

The incidence of cancer increases with age in humans and in laboratory animals alike. There are different patterns of age-related distribution of tumors in different organs and tissues. Aging may increase or decrease the susceptibility of various tissues to initiation of carcinogenesis and usually facilitates promotion and progression of carcinogenesis. Aging may predispose to cancer in two ways: tissue accumulation of cells in late stages of carcinogenesis and alterations in internal homeostasis, in particular, alterations in immune and endocrine systems. Increased susceptibility to the effects of tumor promoters is found both in aged animals and aged humans, as predicted by the multistage model of carcinogenesis. Aging is associated with a number of events at the molecular, cellular and physiological levels that influence carcinogenesis and subsequent cancer growth. An improved understanding of age-associated variables impacting on the tumor microenvironment, as well as the cancer cells themselves, will result in improved treatment modalities in geriatric oncology.

Carcinogenesis and aging 20 years after: escaping horizon

Carcinogenesis is a multistage process: neoplastic transformation implies the engagement of a cell through sequential stages, and different agents may affect the transition between continuous stages. Multistage carcinogenesis is accompanied by disturbances in tissue homeostasis and perturbations in nervous, hormonal, and metabolic factors which may affect antitumor resistance. The development of these changes depends on the susceptibility of various systems to a carcinogen and on the dose of the carcinogen. Changes in the microenvironment may condition key carcinogenic events and determine the duration of each carcinogenic stage, and sometimes they may even reverse the process of carcinogenesis. These microenvironmental changes influence the proliferation rate of transformed cells, the total duration of carcinogenesis and, consequently, the latent period of tumor development. Aging may increase or decrease the susceptibility of various tissues to initiation of carcinogenesis and usually facilitates promotion and progression of carcinogenesis. Aging may predispose to cancer by two mechanisms: tissue accumulation of cells in late stages of carcinogenesis and alterations in internal homeostasis, in particular, alterations in immune and endocrine system. Aging is associated with number of events at molecular, cellular and physiological levels that influence carcinogenesis and subsequent cancer growth.

Cancer in rodents: does it tell us about cancer in humans?

Information obtained from animal models (mostly mice and rats) has contributed substantially to the development of treatments for human cancers. However, important interspecies differences have to be taken into account when considering the mechanisms of cancer development and extrapolating the results from mice to humans. Comparative studies of cancer in humans and animal models mostly focus on genetic factors. This review discusses the bio-epidemiological aspects of cancer manifestation in humans and rodents that have been underrepresented in the literature.

The relationship between aging and carcinogenesis: a critical appraisal

The incidence of cancer increases with age in humans and in laboratory animals alike. There are different patterns of age-related distribution of tumors in different organs and tissues. Aging may increase or decrease the susceptibility of various tissues to initiation of carcinogenesis and usually facilitates promotion and progression of carcinogenesis. Aging may predispose to cancer by several mechanisms: (1) tissue accumulation of cells in late stages of carcinogenesis; (2) alterations in homeostasis, in particular, alterations in immune and endocrine system and (3) telomere instability linking aging and increased cancer risk. Increased susceptibility to the effects of tumor promoters is found both in aged animals and aged humans, as predicted by the multistage model of carcinogenesis. Available evidence supporting the relevance of replicative senescence of human cells and telomere biology to human cancer seems quite strong, however, the evidence linking cellular senescence to human aging is controversial and required additional studies. Data on the acceleration of aging by carcinogenic agents as well as on increased cancer risk in patients with premature aging are critically discussed. In genetically modified mouse models (transgenic, knockout or mutant) characterized by the aging delay, the incidence of tumors usually similar to those in controls, whereas the latent period of tumor development is increased. Practically all models of accelerated of aging in genetically modified animals show the increase in the incidence and the reduction in the latency of tumors. Strategies for cancer prevention must include not only measures to minimize exposure to exogenous carcinogenic agents, but also measures to normalize the age-related alterations in internal milieu. Life-span prolonging drugs (geroprotectors) may either postpone population aging and increase of tumor latency or decrease the mortality in long-living individuals in populations and inhibit carcinogenesis. At least some geroprotectors may increase the survival of a short-living individuals in populations but increase the incidence of malignancy.

Use of historical control data in carcinogenicity studies in rodents

This paper considers the use of historical control data in the evaluation of tumor incidences from carcinogenicity studies in rodents. Although the most appropriate control group for interpretative purposes is always the concurrent control, there are instances in which the use of historical control information can aid an investigator in the overall evaluation of tumor incidence data. One example is rare tumors; another is a tumor that shows a marginally significant result relative to concurrent controls. However, before historical control data can be used in a formal testing framework, a number of important issues must first be considered. The nomenclature conventions and diagnostic criteria for each study should be identical to insure unambiguous identification of all relevant tumors in the historical control database. Criteria should be established that will aid in determining whether a particular study should be included in the database. This will assure a homogeneous set of studies upon which to base statistical comparisons. Since study-to-study variability in tumor rates may exceed what would be expected by chance alone, these sources of variability should be identified and controlled. Finally, statistical procedures should be employed that adjust for extra-binomial variability. This paper also summarizes tumor incidence data from untreated Fischer 344 rats and B6C3F1 mice in the National Toxicology Program (NTP) historical control database. All studies in the database are of two years duration, and all neoplasms occurring with a frequency of 0.5% or more are reported.

Spontaneous neoplasm incidences in Fischer 344 rats and B6C3F1 mice in two-year carcinogenicity studies: a National Toxicology Program update

Spontaneous neoplasm rates were determined for control Fischer 344 (F344) rats and B6C3F1 mice from 2-yr rodent carcinogenicity studies carried out by the National Toxicology Program (NTP). The most frequently occurring neoplasms in untreated male F344 rats were testicular adenoma (89.1%), mononuclear cell leukemia (50.5%), adrenal gland pheochromocytoma (31.9%), and pituitary gland neoplasms (30.4%). For untreated female F344 rats, the most frequently occurring neoplasms were pituitary gland neoplasms (54.2%), mammary gland fibroadenoma (41.2%), and mononuclear cell leukemia (28.1%). The most frequently occurring neoplasms in untreated male B6C3F1 mice were liver adenoma/carcinoma (42.2%), lung adenoma/carcinoma (20.5%), and malignant lymphoma (8.3%). For untreated female B6C3F1 mice, the most frequently occurring neoplasms were liver adenoma/carcinoma (23.6%), malignant lymphoma (20.9%), and pituitary gland adenoma/carcinoma (14.8%). The tumor rates observed in feeding study (untreated) and inhalation study (chamber) control rats were generally similar. The major exceptions were pituitary gland tumors and testicular adenoma in male F344 rats. The overall incidence of testicular adenoma was much lower in chamber controls (69.4%) than in feeding study controls (89.1%), whereas pituitary gland neoplasm showed the opposite trend (60.7% vs 30.4%). The most likely explanation for this difference is related to the individual housing of chamber controls and the group housing of feeding study controls. Differences in diagnostic criteria may influence reported tumor rates. To ensure consistency and comparability of tumor diagnosis from study to study, the NTP uses rigorous histopathology quality assurance and peer review procedures. Biological factors such as body weight may also affect tumor incidence. For example, increased body weights are associated with increased incidences of certain site-specific neoplasms, especially pituitary gland and mammary gland neoplasms in rats and liver tumors in mice. The presence of Helicobacter hepaticus has been associated with an increased incidence of liver neoplasms in male B6C3F1 mice. Other factors that may produce differences in control tumor rates from study to study include diet, environmental factors, genetic drift, study duration, and survival differences. The NTP database provides historical control data that may be useful in the evaluation of possible chemically related changes in tumor incidence. However, it is essential that the study being evaluated be comparable to those in the NTP database with respect to those factors that are known to influence tumor occurrence.

Proliferative pituitary lesions in rats treated with salmon or porcine calcitonin

Calcitonin, the serum calcium-lowering hormone, has been used in the treatment of hypercalcemia of malignancy and postmenopausal osteoporosis in humans for several years without any adverse effects. Recent studies in rats have indicated that calcitonin may be associated with morphologic effects on the pituitary. A large study was performed on 2 strains of rats, Sprague-Dawley (SD) and Fischer-344 (F-344), with 2 types of calcitonin, salmon-derived (sCT) and porcine-derived (pCT) calcitonin to evaluate possible effects on the pituitary. Sixteen groups of 42 male and 42 female SD or F-344 rats were given 0 (vehicle control), 1.25, 5.0, or 80.0 IU/kg/day of sCT or pCT, once daily, subcutaneously, for 1 yr. An increased incidence of adenomas of the adenohypophysis was observed in male SD rats at all dose levels of sCT, female SD rats given 80 IU/kg/day of sCT, male SD rats at the high dose level of pCT, and male F-344 rats at the high dose level of sCT. Also, an increased incidence of total proliferative lesions, due mostly to an increased incidence of focal hyperplasia of the pars distalis, occurred in female F-344 rats given the high dose of sCT. These pituitary proliferations were histologically similar to those that occur spontaneously, and the incidences observed were comparable to those that could occur in rats on 2-yr or lifetime studies, indicating that the injection of calcitonin had decreased the latency period.

Spontaneous neoplasms in aged CD-1 mice

Spontaneous neoplasms in untreated control CD-1 mice (725 males and 725 females) used in carcinogenicity studies were evaluated and tabulated. The most common neoplasms in male mice were alveolar-bronchiolar adenomas (19.3%) followed by hepatocellular adenomas (11.0%), lymphoreticular neoplasms (6.8%), hepatocellular carcinomas (5.7%), Harderian gland adenomas (2.9%), alveolar-bronchiolar carcinomas (2.5%), and testicular interstitial cell tumors (1.9%). In the females, the most frequently occurring neoplasms were lymphoreticular neoplasms (16.4%) followed by alveolar-bronchiolar adenomas (12.3%), uterine endometrial polyps (4.3%), uterine leiomyomas (3.5%), mammary adenocarcinomas (2.5%), hepatocellular adenomas (1.8%), hemangiomas (1.7%), Harderian adenomas (1.7%), alveolar-bronchiolar carcinomas (1.5%), and pituitary adenomas (1.1%). Tumors in other various organs were found at a low incidence.

Spontaneous neoplasms in aged control Fischer 344 rats

Neoplastic lesions in untreated F-344 rats (740 males and 740 females) used as controls in carcinogenicity studies were evaluated and tabulated. The incidence of spontaneous tumors was 84.3% in the males and 76.2% in the females. In males, the most common neoplasms were testicular interstitial cell tumors (79.5%) followed by mononuclear cell leukemia/lymphomas (30.5%), pituitary adenomas (20.5%), pancreatic islet cell adenomas (6.5%), thyroid c-cell adenomas (5.7%), pheochromocytomas (5.7%), skin fibromas (3.2%), keratoacanthomas (1.9%), and thyroid follicular cell adenomas (1.9%). In females, the most common neoplasms were pituitary adenomas (30.3%) followed by mononuclear cell leukemia/lymphomas (20.5%), endometrial polyps (14.1%), mammary fibroadenomas (11.1%), thyroid c-cell adenomas (5.1%), mammary adenomas (1.9%), skin fibromas (1.1%), and clitoral carcinomas (1.1%). A variety of less common neoplasms were also observed in various other organs.

Long-term, low-level microwave irradiation of rats

Our goal was to investigate effects of long-term exposure to pulsed microwave radiation. The major emphasis was to expose a large sample of experimental animals throughout their lifetimes and to monitor them for effects on general health and longevity. An exposure facility was developed that enabled 200 rats to be maintained under specific-pathogen-free (SPF) conditions while housed individually in circularly-polarized waveguides. The exposure facility consisted of two rooms, each containing 50 active waveguides and 50 waveguides for sham (control) exposures. The experimental rats were exposed to 2,450-MHz pulsed microwaves at 800 pps with a 10-microseconds pulse width. The pulsed microwaves were square-wave modulated at 8-Hz. Whole body calorimetry, thermographic analysis, and power-meter analysis indicated that microwaves delivered at 0.144 W to each exposure waveguide resulted in an average specific absorption rate (SAR) that ranged from 0.4 W/kg for a 200-g rat to 0.15 W/kg for an 800-g rat. Two hundred male, Sprague-Dawley rats were assigned in equal numbers to radiation-exposure and sham-exposure conditions. Exposure began at 8 weeks of age and continued daily, 21.5 h/day, for 25 months. Animals were bled at regular intervals and blood samples were analyzed for serum chemistries, hematological values, protein electrophoretic patterns, thyroxine, and plasma corticosterone levels. In addition to daily measures of body mass, food and water consumption by all animals, O2 consumption and CO2 production were periodically measured in a sub-sample (N = 18) of each group. Activity was assessed in an open-field apparatus at regular intervals throughout the study. After 13 months, 10 rats from each group were euthanatized to test for immunological competence and to permit whole-body analysis, as well as gross and histopathological examinations. At the end of 25 months, the survivors (11 sham-exposed and 12 radiation-exposed rats) were euthanatized for similar analyses. The other 157 animals were examined histopathologically when they died spontaneously or were terminated in extremis.

Spontaneous neoplasms in B6C3F1 mice

Spontaneous neoplasms in untreated B6C3F1 mice (200 males and 200 females) used as controls in 4 carcinogenicity studies were evaluated and tabulated. The most common neoplasms in male mice were hepatocellular adenomas/carcinomas (24.5%) followed by alveolar-bronchiolar adenomas/carcinomas (10.0%), lymphoreticular neoplasms (7.0%) [malignant lymphomas mixed (4.5%), histiocytic sarcomas (3.5%)], harderian gland adenoma (6.5%), and hemangiomas/hemangiosarcomas (5.5%). In the females, the most frequently occurring neoplasms were lymphoreticular neoplasms (22.0%) [malignant lymphoma mixed (10.0%), malignant lymphoma lymphocytic (6.5%), histiocytic sarcomas (5.5%)] followed by pituitary adenomas (15.5%), alveolar-bronchial adenomas/carcinomas (11.5%), hepatocellular adenomas/carcinomas (7.0%), harderian gland adenomas, uterine stromal polyps (2.5%), and hemangiomas/hemangiosarcoma (2.0%). The incidence of tumors in various other organs was found to be low.

Carcinogenicity study of methyl hesperidin in B6C3F1 mice

A long-term carcinogenicity study of methyl hesperidin, a compound of the vitamin P group, was carried out in B6C3F1 mice receiving dietary concentrations of 0, 1.25 or 5%. Administration was continued for 96 wk and then the mice were maintained on basal diet for an additional 8 wk. Growth retardation during the experiment with final changes in organ weights were observed in females given the 1.25% dose of methyl hesperidin and in both sexes receiving the 5.0% treatment. However, no biologically significant effects were evident with respect to mortality or clinical signs. Furthermore, treatment with methyl hesperidin did not result in any changes in haematology, clinical chemistry and urinalysis data. On histological examination, no significant alteration of non-neoplastic and neoplastic lesion incidence was observed in treated mice. The results thus demonstrated that methyl hesperidin lacked any carcinogenicity for B6C3F1 mice in the 96-wk feeding regimen used in this study.

Inhibitory effects of chlorogenic acid, reserpine, polyprenoic acid (E-5166), or coffee on hepatocarcinogenesis in rats and hamsters

Four different experiments were performed in order to examine the modifying effects of chlorogenic acid (CA), reserpine, polyprenoic acid (E-5166), and coffee on chemical carcinogenesis in rats or hamsters. Experiment 1: The numbers of hyperplastic liver cell foci and the incidence of colon tumors in male and female Syrian golden hamsters given a single intravenous injection of methylazoxymethanol (MAM) acetate and then fed the diet containing 0.025% CA for 24 wk were significantly lower than those of hamsters given MAM acetate alone. Experiment 2: The incidence of altered hepatocellular foci in female ACI/N rats given N-2-fluorenylacetamide (FAA, 0.02% in diet) for 10 wk and reserpine (weekly subcutaneous injections, 1 microgram/g body weight) during or after (17 wk) FAA exposure was significantly lower than that of rats given FAA alone. Experiment 3: The number of hepatocellular foci in male ACI/N rats given 0.02% FAA diet for 13 wk and E-5166 by gavage (40 mg/kg body weight, 3 times/wk) for 16 wk after the end of FAA exposure was significantly smaller than that in rats given FAA diet alone. Experiment 4: Incidences of liver tumors and hepatocellular foci of rats given concurrent dietary administration of aminopyrine (0.01%) and sodium nitrite (0.1%) and coffee solution as a drinking water for 630 da were significantly lower than those of rats given aminopyrine and sodium nitrite. Thus, the tested compounds had inhibitory effects on chemical carcinogenesis in liver or colon.

The interpretation of equivocal or marginal animal carcinogenicity tests

The interpretation of animal carcinogenicity tests traditionally rely almost exclusively upon a comparison of specific tumor rates in treated vs. matched and, perhaps, historical control animals. Yet, carcinogenicity tests yield much more biological and pathological data than simply final tumor rates. This additional data should also be considered as part of the total weight of evidence, particularly when analyzing a marginal or equivocal test result. If there are no positive findings among the data discussed here and listed in Table 1, it is unlikely that a marginal or equivocal increase in tumor incidence is actually treatment-related, irrespective of statistical analysis.

Chlordane: 24-month tumorigenicity and chronic toxicity test in mice

Four groups of 80 ICR SPF mice of each sex were fed 0-12.5 ppm technical chlordane for 104 weeks. Male and female mice were examined for hematological, biochemical, urinary, and pathological changes at 52 and 104 weeks of exposure. Serum AST (= SGOT) and ALT (= SGPT) were elevated in treated males and females, liver weights were increased in the 12.5-ppm groups, and masses were seen in the livers of 12.5-ppm males. Increased liver cell volume was seen in 5- and 12.5-ppm males and females, while hepatocyte degeneration and necrosis were seen only in treated males. Hepatic hemangiomas and hepatocellular adenomas typically occurred together and were significantly increased in 12.5-ppm males. No other significant changes were detected. However, the incidence of tumors in the 12.5-ppm males was within the range of historical controls. Accordingly, there was no evidence that chlordane induced tumors in the ICR mice. A long-term no-observed-effect level (NOEL) of 1 ppm chlordane in the diet was found.

Spontaneous tumors in aging (C57BL/6N x C3H/HeN)F1 (B6C3F1) mice

Spontaneous tumors in untreated (C57BL/6N x C3H/HeN)F1 (B6C3F1) mice used as controls in carcinogenicity tests were recorded. In both sexes, the development of spontaneous tumors was age-related. In 244 male mice, the most common tumors were hyperplastic nodules of the liver, hepatocellular carcinomas, malignant lymphomas/leukemias, lung adenomas, and adenocarcinomas. In 246 female mice, the most common tumors were malignant lymphomas/leukemias, pituitary adenomas, neoplastic nodules of the liver, hepatocellular carcinomas, and lung adenomas. Hepatocellular carcinomas metastasized in 20.3% of the animals with these tumors. Few other tumors except malignant lymphomas and leukemias metastasized. Various tumors of other organs and/or tissues were found at low incidences.

Age-related increased susceptibility of male Fischer 344 rats to acetaminophen nephrotoxicity

Male Fischer 344 rats classified as young (2-4 months), middle-aged (12-14 months) and aged (22-25 months) received 300, 600 or 800 mg/kg acetaminophen (APAP) intraperitoneally and were sacrificed 24 hr later. Blood urea nitrogen (BUN) concentration and urinary glucose and osmolality were determined. In addition, kidneys were evaluated for histopathological changes. APAP did not affect osmolality or BUN concentrations and failed to produce lesions after any dose in young rats. Osmolality was decreased 40% and 50% in middle-aged and aged rats, respectively, after 800 mg/kg APAP. Glucosuria was prominent in aged rats after the 600 and 800 mg/kg doses were administered, while middle-aged rats showed little glucosuria after these doses. BUN concentrations were elevated 89% and 183% in middle-aged and aged rats, respectively, given 600 mg/kg APAP; after 800 mg/kg, BUN concentrations were elevated approximately four-fold in both age groups. Pathological evaluations showed a greater incidence of acute tubular necrosis (ATN) in aged kidneys compared to kidneys of middle-aged rats after 600 mg/kg, while the two older groups exhibited similar, more severe ATN after 800 mg/kg APAP. These data suggest an age-related increased susceptibility of male Fisher 344 rats to APAP nephrotoxicity.

The development of acetaminophen-induced nephrotoxicity in male Fischer 344 rats of different ages

Male Fischer 344 rats classified as young (2-4 months), middle-aged (12-15 months) and aged (22-25 months) were administered 600 mg/kg acetaminophen (APAP) IP. Rats were killed 6 and 12 h after dosing, and renal damage evaluated by blood urea nitrogen (BUN) levels and histopathology. In addition, plasma levels of APAP and its sulfate and glucuronide conjugates were determined after 6 h. There was no evidence of renal damage in any age group 6 h after APAP. While no nephrotoxicity was present in young animals after 12 h, BUN was elevated 94% and 214% in middle-aged and aged rats, respectively, compared to young animals. At 12 h, APAP-induced renal lesions were more severe in aged rats compared to middle-aged animals. APAP-induced renal damage, as judged by BUN and histopathology, was not altered in young or middle-aged rats following unilateral nephrectomy. Six hours after APAP, both the middle-aged and aged animals had significantly higher plasma levels of APAP and APAP glucuronide compared to young rats. There were similar amounts of the sulfate conjugate in the plasma of each age group. This suggests pharmacokinetic differences could contribute to the age-related increased susceptibility of male Fischer 344 rats to APAP-induced nephrotoxicity.

Profiles of induced tumors in animals

Chemical carcinogens often induce neoplasms which differ qualitatively and quantitatively from tumors that occur spontaneously in the tissue of interest. While some experimental models have produced neoplasms indistinguishable from their spontaneous counterparts, most cause growths that are histogenetically or morphologically different, larger, more numerous, more aggressive, or of shorter latency. Induced tumors may occur in tissues where spontaneous tumors are uncommon. Cells of induced tumors may express phenotypic characteristics (e.g., membrane antigens) not present in corresponding nonneoplastic or spontaneously neoplastic cells. Conversely, some characteristics present in normal or spontaneously neoplastic cells (e.g., certain enzyme activity) may be absent in induced neoplasms. Not only may carcinogens induce tumors that differ from spontaneous ones, but the effect or a particular carcinogen may vary with the condition of its use. The species of strain, sex, and age of the host as well as the dose and route of administration are major variables. Neoplasia is one result of altered cell regulation. If we postulate a central dogma for oncogenensis, induced tumors should arise from the same molecular mechanisms that produce spontaneous tumors. Differences in "profile" reside not in the ultimate mechanism, but in the events which surround it. They result from the myriad of factors which determine the dose of proximal carcinogen to the cell's sensitive volume, together with those that modify subsequent proliferation and differentiation.

Factors influencing laboratory animal spontaneous tumor profiles

In chemical carcinogenicity and drug-safety testing, a carcinogen is defined as an agent that when administered by an appropriate route causes an increased incidence of tumors in experimental animals as compared to unexposed control animals. Although a carcinogen may cause the appearance of tumors in organs where tumors do not usually occur in a given strain, the usual response is to increase the types of tumors seen spontaneously and to shorten the period of latency. The use of carcinogenesis experiments for research and safety assessment requires properly designed and well-conducted experiments and a knowledge of background data and variations in tumor incidences of control animals. Many factors can influence the reported incidences of spontaneous tumors. These include species, strain, sex, age, and source of the experimental test animal; study duration; extent of the pathology examination; dietary and environmental conditions; qualifications and experience of the study pathologist; diagnostic criteria and nomenclature conventions; and quality assurance and review procedures. This paper discusses several factors which may influence the incidence of tumors in control and test animals, and provides examples to illustrate the potential for these factors to affect the data.

Incidence of spontaneous tumors in laboratory rats

The Caw-Hoe-Wiga strain of the Sprague-Dawley rat was observed for a period of ten years (1974--1983). In toxicity studies, a gradual increase of food intake could be noted in 12- to 13-week-old rats. The food intake of males was 21 g in 1974 and 27 g in 1983; in females 16 g in 1974 and 19 g in 1984. Correspondingly, a gradual increase of body weight was measured. The body weight of males was 400 g in 1974 and 470 g in 1983; of females 240 g in 1974 and 285 g in 1983. The gradual increase of food intake and body weight was followed by a gradual increase in the incidence of spontaneous tumors, 1974: 5% and 1983: 13%. Our experiments support the opinion of a causal connection between food intake, body weight and incidence of spontaneous tumors. Tumors can appear in any age group, but tumors. occur more often in older animals. In our studies, the increase in the incidence of spontaneous tumors was proportional to the increase in age: At 15 months only 6%, at 32 months 86%. 32% of the tumors were located in the mammary glands, 27% in the hypophysis, 12% in skin and appendages, and 9% in other endocrine organs. The comparison of toxicity and carcinogenicity studies revealed no change in the tumor spectrum, but strain-related tumors appeared earlier in life, more frequently and more often multifocally towards the end of the 10-year observation period.(ABSTRACT TRUNCATED AT 250 WORDS)

The early stage of large granular lymphocyte leukemia in the F344 rat

In the early stages of large granular lymphocyte leukemia of F344 rats, splenic congestion and lymphocytic depletion of the splenic white pulp are the most significant and consistent histologic findings. The diagnosis of early leukemia was confirmed by immunocytochemical demonstration that the cell surface of leukemic large granular lymphocytes reacted with OX-8 monoclonal antibodies and by transplantation of the disease at early stages to healthy weanling rats.