Carcinogenicity of glycidol in F344 rats and B6C3F1 mice.

Glycidol, a simple aliphatic epoxide, was administered by gavage in water to groups of male and female F344/N rats and B6C3F1 mice. Rats received 0, 37.5 or 75 mg kg-1 and mice received 0, 25 or 50 mg kg-1 daily, 5 days per week for 2 years. Exposure to glycidol was associated with dose-related increases in the incidences of neoplasms in numerous tissues in both rats and mice. Survival of rats that received glycidol was markedly reduced compared to the control because of the early induction of neoplastic disease. In male rats, mesothelioma arising in the tunica vaginalis and frequently metastasizing to the peritoneum were considered the major cause of early death. Early deaths in female rats were associated with mammary gland neoplasms. Survival of female mice that received 50 mg kg-1 was lower than the control after week 101 due primarily to euthanasia of moribund animals with mammary gland neoplasms. Survival of male mice and female mice that received 25 mg kg-1 was comparable to the control. In mice, exposure to glycidol was associated with increased incidences of neoplasms of the harderian gland in males and females, the forestomach in males and the mammary gland in females.

Proliferating cell nuclear antigen staining of Fischer-344/N rat spleens affected by large granular lymphocyte leukemia.

Large granular lymphocyte (LGL) leukemia commonly occurs in the Fischer-344/N rat. The high spontaneous incidence complicates the interpretation of results from chronic carcinogenicity studies that use this rat strain. As a result, a comprehensive characterization of LGL leukemia is necessary to help understand the leukemogenic process and the applicability of staging for assessing the progression of this disease. In the current study, the proliferation rate of LGL leukemia cells from untreated control Fischer-344 (F-344) rats in 3 stages of leukemia compared to nonleukemic age-matched rats was determined by immunohistochemical staining for proliferating cell nuclear antigen (PCNA). In histologic sections of spleen from aged F-344/N rats affected by LGL leukemia, there was a significant increase of both PCNA labeling and mitotic indices that was most advanced in the spleen of rats with more severe LGL leukemia. These results support biological significance for the morphologic staging system currently in use.

The A/J mouse lung as a model for developing new chemointervention strategies.

The use of the A/J mouse lung as a model for developing new chemo-intervention strategies was investigated by first inducing lung tumors with a single dose of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone. Lungs were then staged for tumor development and intervention therapy was initiated 42 weeks after carcinogen treatment. At this time point, an average of 7 pulmonary lesions were present on a standard histological section and the relative frequency of lesions was distributed as alveolar hyperplasias (38%), adenomas (40%), and adenocarcinomas (22%). Mice were treated for 4 or 8 weeks with cis-platinum alone or in combination with either indomethacin, an inhibitor of prostaglandin synthesis, metoclopramide, an inducer of poly(ADP) ribosylation, or nifedipine, a calcium channel blocker. The effect of indomethacin, metoclopramide, and nifedipine on tumor growth was also determined. The most dramatic effects were observed in lungs from mice treated for 8 weeks. cis-Platinum treatment caused a 37% reduction in the size of carcinomas, while tumor mass was reduced by 50 to 60% with cis-platinum in combination with metoclopramide and/or indomethacin. The inclusion of indomethacin therapy in conjunction with cis-platinum significantly enhanced the effectiveness of cis-platinum for inhibiting the growth of adenocarcinomas. In contrast, nifedipine appeared to ameliorate any of the inhibitory growth effects seen with cis-platinum treatment. Although none of the therapeutic combinations affected the size of adenomas, morphological differences were observed among treatment groups. A moderate to marked decrease in cytoplasm was observed in adenomas from mice treated with cis-platinum in combination with indomethacin or metoclopramide, cis-platinum plus metoclopramide and indomethacin, or metoclopramide plus indomethacin. Taken together, the results from these studies demonstrate that the A/J mouse lung can be used as a model to study the effectiveness of new intervention therapies for controlling malignant tumor growth. This model should also be applicable for studying the effectiveness of cancer prevention therapies on the progression of pulmonary hyperplasia.

Comparative acute nephrotoxicity of salicylic acid, 2,3-dihydroxybenzoic acid, and 2,5-dihydroxybenzoic acid in young and middle aged Fischer 344 rats.

Experimental evidence suggests that the oxidative metabolites 2,3- and 2,5-dihydroxybenzoic acid (DIOH) may be responsible for the nephrotoxicity of salicylic acid (SAL). In the present study, enzymuria in conjunction with glucose (GLU) and protein (PRO) excretion were used as endpoints to compare the relative nephrotoxicity of SAL with 2,3- and 2,5-DIOH. In addition, the effect of age on enzymuria and GLU and PRO excretion following treatment with SAL or 2,3- and 2,5-DIOH was investigated because the elderly are at greater risk for SAL-induced nephrotoxicity. Three and 12-month male Fischer 344 rats were administered either no treatment, vehicle, SAL, 2,3-DIOH, or 2,5-DIOH at 500 mg/kg p.o. in 5 ml/kg corn oil/DMSO (5:1). Effects of these treatments on functional integrity of renal tissue was assessed from 0--72 h after dosing by measurement of urinary creatinine, GLU, and PRO, as well as excretion of proximal and distal tubular renal enzymes. Enzymes measured as indicators of proximal tubular damage were N-acetyl-beta-glucosaminidase (NAG), gamma glutamyltransferase (GGT), alanine aminotransferase (ALT), and alkaline phosphatase (AP), while urinary lactate dehydrogenase (LD) and aspartate aminotransferase (AST) were measured as indicators of distal tubular damage. In comparison to 3-month vehicle-treated rats, 2,3- and 2,5-DIOH caused a significant increase between 0-8 h in excretion of urinary GLU and activities of AST, NAG, and LD, with peak effects occurring between 4-8 h. Toxic effects of either metabolite were not evident beyond 24 h, and toxicity of 2,5-DIOH was significantly greater in comparison to 2,3-DIOH. SAL treatment resulted in similar effects on enzymuria as well as GLU and PRO excretion, but peak effects did not occur until 16-24 h, and often persisted until 72 h after dosing. Maximal enzymuria in response to SAL treatment was significantly greater in 12- vs. 3-month rats for AST, NAG, and LD. In response to 2,3-DIOH treatment, the maximal response was significantly greater in 12- vs. 3-month rats for LD and AST, and for NAG in response to 2,5-DIOH treatment. The results of this study suggest that both 2,3- and 2,5-DIOH are nephrotoxic metabolites of SAL, but implicate 2,5-DIOH as the more potent nephrotoxic metabolite. The relative lack of an age effect for 2,3- and 2,5-DIOH vs. SAL supports the hypothesis [2] that age-related differences in biotransformation of SAL, and not increased tissue sensitivity to 2,3- or 2,5-DIOH, contribute to the age-related increase in susceptibility to SAL-induced nephrotoxicity.

Development and validation of a cellular transplant model for leukemia in Fischer rats: a short-term assay for potential anti-leukemic chemicals.

The efficacy of a leukemia cell transplant model to measure potential chemotherapeutic activity was tested with five different chemicals that had previously been evaluated in 2-year studies. Leukemic spleen cells from Fischer rats were injected subcutaneously into syngeneic recipients and the effects of chemical treatment on tumor progression were evaluated at 70 days post-transplant. The data from the short-term assay were in all cases correlated with the trends reported for mononuclear cell leukemia in 2-year studies, where two chemicals were reported to decrease the incidence and three chemicals were reported to increase the incidence of leukemia. Short-term treatment with the two chemicals which caused negative trends for leukemia (2-ethoxyethanol or ethylene glycol monoethyl ether; 4-hexylresorcinol) delayed and/or reduced tumor growth in the transplant model in a dose-related fashion, as exhibited by reduction or elimination of splenomegaly and leukoblastosis, and a reversal in the depression of red blood cell indices or platelet counts. By contrast, the rate of tumor progression was increased in the short-term assay of the three chemicals which previously caused increased trends for leukemia in 2-year studies (pyridine; 2,4,6-trichlorophenol, dichlorvos). The severity of the mononuclear cell leukemia in the transplant recipients, as measured by histopathological examination of spleen and liver, was correlated with the changes in tumor growth rates. The in vivo leukemia transplant model is a short-term assay that could be used to screen a variety of potential chemotherapeutic agents, or to study structure-activity relationships within one class of chemicals.

Testicular toxicity and reduced Sertoli cell numbers in neonatal rats by di(2-ethylhexyl)phthalate and the recovery of fertility as adults.

Neonatal and adult rats (1, 2, 3, 6, and 12 weeks of age) were given five daily oral doses of di(2-ethylhexyl) phthalate (DEHP) (0, 10, 100, 1000, 2000 mg/kg) and histological changes in the testes were examined 24 hr after the last dose. Relative testis weights were reduced at doses of 1000 mg/kg in 1, 2, 3, and 6-week-old but not in 12-week-old rats, while doses of 2000 mg/kg were fatal to suckling rats and caused decreased relative testis weight but not death in 6- and 12-week-old rats. In neonatal rats (1 week old), DEHP (1000 mg/kg) caused a 35% decrease in Sertoli cell numbers while 2- and 3-week-old rats showed losses of spermatocytes but not of Sertoli cells. The 6- and 12-week-old rats showed loss of both spermatids and spermatocytes at 1000 and/or 2000 mg/kg. Total testicular zinc concentrations were decreased in 12-week-old but not in suckling (3-week) or weaned (6-week) rats. The results support the hypothesis that the Sertoli cell is the primary testicular target of phthalate ester toxicity since effects were observed at an age when only Sertoli cells were present. Fertility was assessed in mating trials in adult male rats after neonatal exposure to DEHP on Days 6-10. Although Sertoli cell number was reduced 24 hr after the last dose, the numbers were normal at 6 and 13 weeks of age. However, at 6 weeks there was a dose-related decrease in maturation of the spermatids in the tubules. There were no consistent changes in fertility, implantation rate, or numbers of live fetuses in untreated females mated with the DEHP-treated males. However, there were decreases in testis weight and testicular spermatid numbers at 13 and 19 weeks but not at 11, 12, 16, or 23 weeks of age. Therefore, a loss of Sertoli cells due to DEHP exposure neonatally did not affect the fertility of the rats as adults, but may have caused subtle effects on sperm production.

The effect of age on the glucuronidation and toxicity of 4,4'-thiobis(6-t-butyl-m-cresol).

Age-related changes in glucuronidation may potentially lead to a decrease in excretion of reactive compounds, resulting in enhanced toxic effects. 4,4'-Thiobis(6-t-butyl-m-cresol) (TBBC), a major antioxidant in the rubber industry, was selected as a model compound to evaluate glucuronidation as a function of age because it is directly conjugated to UDP-glucuronic acid (UDPGA) without requiring oxidative metabolism. To assess glucuronidation changes in vivo, male F344 rats, 2.5, 16, and 26 months of age, were administered 5 mg [14C]-TBBC/kg (10 microCi/kg) iv and urine and feces were collected for 3 days. Bile was also collected for 6 hr from animals of the same age groups after iv doses of 5 and 25 mg/kg [14C]TBBC. Total radioactivity was determined in all samples and the profile of metabolites in bile analyzed by HPLC. Along with a decrease in the older animal's ability to excrete TBBC-derived radioactivity in bile, feces, and urine, there was a decrease in the percentage of the dose eliminated in bile as glucuronide. In vitro, the microsomal glucuronyltransferase activity using TBBC as a substrate decreased in the senescent animals. The hepatic concentration of the cofactor UDPGA also decreased from 2.5 to 28 months of age. The apparent Vmax for the enzyme decreased as a function of age while the apparent Km decreased for the substrate (TBBC) but not for the cofactor (UDPGA) in the 26-month-old rats. These data suggest that with the decrease in the activity of the enzyme as well as a decrease in the available UDPGA, the ability of the senescent rats to conjugate and excrete TBBC may be altered. Thus, the in vitro decline in TBBC glucuronidation is compatible with the decreased excretion of TBBC-derived radioactivity observed in vivo in old rats. When toxicity was evaluated in 2.5-, 16-, and 26-month-old rats exposed to 0.25% TBBC in their diet for 14 days, no age-related change in the toxicity of TBBC was observed. However, there appeared to be an increase in leukemia in the treated senescent rats.

Chordomas in Fischer 344 rats.

Tissue sections and records of 56 rats with chordoma, identified in the National Toxicology Program's (NTP) data base of approximately 115,000 rats, were examined to determine morphological characteristics, incidence, and aspects of biological behavior. Chordomas occurred in aged rats, originated predominantly in lumbosacral vertebrae, were highly malignant, occurred three times more often in male versus female rats, and commonly produced bilateral posterior paresis, paralysis, and/or distention of the colon and rectum.

Effect of methyl isocyanate (MIC) gas on the eyes of Fischer 344 rats.

The accidental release of methyl isocyanate gas in Bhopal, India, was reported to cause temporary blindness and other eye injuries in many of the exposed people. Methyl isocyanate (MIC) is known to be corrosive and to irritate intact skin and mucous membranes, but little is known about the extent of ocular damage incurred during exposure to its vapors. The eyes of male and female Fischer 344 rats were evaluated immediately after a 2-hr exposure to 0, 3, 10, or 30 ppm of MIC, and periodically thereafter during a 91-day recovery period. During exposure to 10 ppm and higher concentrations, rats kept their eyes partially closed. Copious lacrimation and occasional frothy nasal discharge were evident. Eyes were examined under ultraviolet light after topical application of sodium fluorescein, and histopathologic examination included lids, cornea, lens, retina, optic nerve, and Harderian gland. There was no significant gross or microscopic evidence of epithelial erosion or ulceration of the cornea, or of adjacent tissues immediately after, or at any time following exposures. No skin irritation was noted. It would appear that the natural protective mechanisms of the eye of rats were adequate to prevent ocular damage at these exposure levels.

Two-hour methyl isocyanate inhalation exposure and 91-day recovery: a preliminary description of pathologic changes in F344 rats.

The accidental release of methyl isocyanate (MIC) in Bhopal, India, was reportedly responsible for the deaths of more than 2,000 people. To study the pathology of acute inhalation exposure to MIC, the tissues of male and female Fischer 344 rats were evaluated immediately after a single 2-hr exposure to 0, 3, 10, or 30 ppm MIC, and through day 91. Early gross pathologic changes in the 30 ppm-exposed rats included a reddish white encrustation around the mouth and nose, a small thymus, and distension of the gastrointestinal tract with gas. Lungs (middle and median lobes) showed consolidation and hemorrhage and failed to deflate when the chest cavity was opened. Microscopic changes in the upper respiratory tract 3 hr after exposure included marked erosion and separation of olfactory and respiratory epithelia from the basement membrane with accumulation of serofibrinous fluid. On day 1, acute inflammation and fibrinopurulent exudate partially blocked the nasal passages. Epithelial cells had sloughed from the nasopharynx, trachea, bronchi, and major bronchioles, leaving the basement membrane covered with fibrin and exudate. Granulomatous inflammation and intraluminal fibrosis of the airways were observed by day 3, with increased intraluminal fibrosis by day 7. Lower airways became blocked by exfoliated cells, mucous plugs, and/or intraluminal fibrosis.(ABSTRACT TRUNCATED AT 250 WORDS)