Carcinogenicity of inhaled vanadium pentoxide in F344/N rats and B6C3F1 mice.

Vanadium pentoxide (V2O5) is a slightly soluble compound found in airborne particle emissions from metallurgical works and oil and coal burning. Because the carcinogenic potential of V2O5 was not known, F344/N rats and B6C3F1 mice (N=50/sex/species) were exposed to V2O5 at concentrations of 0, 0.5 (rats only), 1, 2, or 4 (mice only) mg/m3, by whole-body inhalation for 2 years. The survival and body weights of rats were minimally affected by exposure to V2O5. The survival and body weights of male mice exposed to 4 mg/m3 and body weights of all exposed groups of female mice were lower than the controls. Alveolar/bronchiolar (A/B) neoplasms occurred in male rats exposed to 0.5 and 2 mg/m3 at incidences exceeding the National Toxicology Program (NTP) historical control ranges. A marginal increase in A/B neoplasms was also observed in female rats exposed to 0.5 mg/m3. Increases in chronic inflammation, interstitial fibrosis, and alveolar and bronchiolar hyperplasia/metaplasia and squamous metaplasia were observed in exposed male and female rats. A/B neoplasms were significantly increased in all groups of exposed mice. As with rats, increases in chronic inflammation, interstitial fibrosis, and alveolar and bronchiolar epithelial hyperplasia were observed in mice exposed to V2O5. Thus, V2O5 exposure was a pulmonary carcinogen in male rats and male and female mice. The marginal tumor response in the lungs of female rats could not be attributed conclusively to exposure to V2O5. These responses were noted at and slightly above the OSHA permissible occupational exposure limit of 0.5 mg/m3 (dust) (National Institute for Occupational Safety and Health, NIOSH Pocket Guide to Chemical Hazards, U.S. Department of Health and Human Services, Washington, DC, 1997, p. 328).

Toxicity and carcinogenicity study in F344 rats following 2 years of whole-body exposure to naphthalene vapors.

The toxicologic and carcinogenic potential of naphthalene was studied by exposing groups of 49 male and 49 female F344 rats to atmospheres containing 0, 10, 30, or 60 ppm of the chemical for 6 h daily, 5 days/wk for 2 yr. Mean body weights of exposed groups of male rats were less than for the control group throughout most of the study. Mean body weights of exposed female rats were generally similar to those of controls. Survival of exposed and control rats was similar. Under the conditions of this 2-yr inhalation study, naphthalene was carcinogenic to male and female F344/N rats, causing increased incidences of respiratory epithelial adenoma (males: control, 0%; low dose, 12%, mid dose, 17%; high dose, 31%; females: 0%; 0%; 8%; 4%) and olfactory epithelial neuroblastoma (males: control, 0%; low dose, 0%; mid dose, 8%; high dose, 6%; females: 0; 4%; 6%; 24%) of the nose. In both sexes of rats, exposure to naphthalene also caused significant increases in the incidences of nasal lesions including hyperplasia, atrophy, chronic inflammation, and hyaline degeneration of the olfactory epithelium and hyperplasia; squamous metaplasia, hyaline degeneration, and goblet-cell hyperplasia of the respiratory epithelium; and glandular hyperplasia and squamous metaplasia.

Effects of glutaraldehyde in a 2-year inhalation study in rats and mice.

Whole-body inhalation toxicology and carcinogenicity studies were performed with the widely used fixative and cold-sterilant glutaraldehyde. Groups of 50 male and female F344/N rats and B6C3F(1) mice were exposed to glutaraldehyde (rats: 0, 250, 500, or 750 ppb; mice: 0, 62.5, 125, or 250 ppb) 6 h/day, 5 days/week, for 104 weeks. Survival of 500- and 750-ppb female rats was less than that of controls. Mean body weights of all exposed groups of male rats, 500- and 750-ppb female rats, and 250-ppb female mice were generally less than those of controls. No exposure-related neoplastic lesions were observed in either rats or mice. Non-neoplastic lesions were limited primarily to the most anterior region of the nasal cavity. In rats, hyperplasia and inflammation of the squamous epithelium; hyperplasia, goblet cell hyperplasia, inflammation, and squamous metaplasia of the respiratory epithelium; and hyaline degeneration of the olfactory epithelium were observed. In mice, the nasal lesions were qualitatively similar to those in rats. Squamous metaplasia of the respiratory epithelium was observed in both sexes of mice while female mice also had inflammation and hyaline degeneration of the respiratory epithelium. In contrast to the nasal carcinogen formaldehyde, no neoplastic lesions were observed after inhalation exposure to glutaraldehyde. However, exposure to glutaraldehyde resulted in considerable non-neoplastic lesions in the noses of rats and mice.

Inhalation toxicity and carcinogenicity studies of cobalt sulfate.

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

Multiple organ carcinogenicity of inhaled chloroprene (2-chloro-1,3-butadiene) in F344/N rats and B6C3F1 mice and comparison of dose-response with 1,3-butadiene in mice.

Chloroprene (2-chloro-1,3-butadiene) is a high production chemical used almost exclusively in the production of polychloroprene (neoprene) elastomer. Because of its structural similarity to 1,3-butadiene, a trans-species carcinogen, inhalation studies were performed with chloroprene to evaluate its carcinogenic potential in rats and mice. Groups of 50 male and female F344/N rats and 50 male and female B6C3F1 mice were exposed to 0, 12.8, 32 or 80 p.p.m. chloroprene (6 h/day, 5 days/week) for 2 years. Under these conditions, chloroprene was carcinogenic to the oral cavity, thyroid gland, lung, kidney and mammary gland of rats, and to the lung, circulatory system (hemangiomas and hemangiosarcomas), Harderian gland, kidney, forestomach, liver, mammary gland, skin, mesentery and Zymbal's gland of mice. Survival adjusted tumor rates in mice were fit to a Weibull model for estimation of the shape of the dose-response curves, estimation of ED10 values (the estimated exposure concentration associated with an increased cancer risk of 10%) and comparison of these parameters with those for 1,3-butadiene. Butadiene has been identified as a potent carcinogen in mice and has been associated with increased risk of lymphatic and hematopoietic cancer in exposed workers. Shape parameter values for most of the neoplastic effects of chloroprene and 1,3-butadiene were consistent with linear or supralinear responses in the area near the lowest tested exposures. The most potent carcinogenic effect of 1,3-butadiene was the induction of lung neoplasms in female mice, which had an ED10 value of 0.3 p.p.m. Since the ED10 value for that same response in chloroprene exposed mice was also 0.3 p.p.m., we conclude that the carcinogenic potency of chloroprene in mice is similar to that of 1,3-butadiene. Cancer potency of chloroprene is greater in the mouse lung than in the rat lung, but greater in the rat kidney than in the mouse kidney and nearly equivalent in the mammary gland of each species.

Lung tumor induction by inhalation exposure to molybdenum trioxide in rats and mice.

Inhalation studies of molybdenum trioxide (MoO3) were conducted because of its wide use in industry, human exposure, and lack of data on carcinogenicity. Groups of 50 male and 50 female F344/N rats and B6C3F1 mice were exposed to MoO3 by inhalation at 0, 10, 30, or 100 mg/m3, 6 h/day, 5 days/week, for 2 years. In both rats and mice, survival and mean body weights of exposed groups of males and females were similar to those of their respective controls. There were significant exposure-dependent increases in blood molybdenum concentration in exposed rats and mice. There were no toxicological differences in bone density or curvature between exposed animals and their respective controls. In rats, dose-dependent increases in incidence of hyaline degeneration in the nasal olfactory epithelium and squamous metaplasia of the epithelium lining the base of the epiglottis were observed. The incidence of alveolar/bronchiolar adenoma or carcinoma (combined) was marginally increased in males but not in females compared with controls. In mice, the incidences of squamous metaplasia of the epithelium lining the base of the epiglottis, hyperplasia of the laryngeal epithelium, and metaplasia of the alveolar epithelium were significantly increased in all exposed males and females compared with controls. The incidence of alveolar/bronchiolar adenoma or carcinoma (combined) in exposed groups of males and females was significantly greater than that in the control groups.

Physiologically based pharmacokinetic model for chronic inhalation of 2-butoxyethanol.

2-Butoxyethanol (2BE) is used extensively in the production of cleaning agents and as a general solvent. It is primarily metabolized in the liver to 2-butoxyacetic acid (2BAA), which is excreted in urine. The objective of this study was to develop a physiologically based pharmacokinetic (PBPK) model describing the toxicokinetic behavior of 2BE and 2BAA in different species following repeated, long-term exposures. The PBPK model was first developed for short-term 2BE exposure to male rats. Allometric scaling was employed to estimate physiological and biochemical model parameters based on body weight. To accommodate differences in 2BE toxicokinetics in female rats, a higher Vmax for 2BE metabolism to 2BAA, higher plasma protein binding sites for 2BAA, and lower Vmax for 2BAA excretion through the kidney were incorporated into the model. For mice, a higher Vmax for 2BE metabolism to 2BAA for both sexes and higher plasma protein binding sites for 2BAA for female mice were also incorporated into the model. Subsequently, the model was expanded to simulate 2BE and 2BAA toxicokinetics for long-term, repeated exposures by incorporating time-dependent changes in model parameters. To reflect physiological/biochemical changes in animals during a chronic exposure, parameters for cardiac output, body composition, metabolic capacity, protein binding, or capacity of renal excretion were adjusted over time depending on species and sex. Sensitivity analysis was performed to better understand how sensitive model responses were to uncertainties in input parameters. The resulting PBPK model was used to simulate toxicokinetic data acquired during a 2-year inhalation toxicity and carcinogenicity study in male and female F344/N rats and B6C3F1 mice.

Toxicokinetics of inhaled 2-butoxyethanol and its major metabolite, 2-butoxyacetic acid, in F344 rats and B6C3F1 mice.

2-Butoxyethanol (2BE) is used extensively in the production of cleaning agents and solvents. It is primarily metabolized in the liver to 2-butoxyacetic acid (2BAA), which is believed to be responsible for 2BE toxicities associated with hemolysis of red blood cells. The objective of the study was to characterize the systemic disposition of 2BE and 2BAA in rats and mice during 2-year 2BE inhalation toxicity studies. Male and female F344 rats and B6C3F1 mice (6-7 weeks old) were exposed to target 2BE concentrations of 0, 31.2, 62.5, or 125 ppm (rats), or 0, 62.5, 125, or 250 ppm (mice), by whole-body inhalation for 6 h/day, 5 days/week for up to 18 months. Postexposure blood samples were collected after 1 day, 2 weeks, and 3, 6, 12, and 18 months of exposure. Postexposure 16-h urine samples were collected after 2 weeks and 3, 6, 12, and 18 months of exposure. A separate set of mice was kept in the control chamber and exposed to 2BE for 3 weeks when they were approximately 19 months old. Postexposure blood samples were collected after 1 day and 3 weeks of exposure and 16-h urine samples were collected after 2 weeks of exposure from these aged mice. Blood samples were analyzed for both 2BE and 2BAA and urine samples were analyzed for 2BAA using GC/MS, and their kinetic parameters were estimated through the curve-fitting method using SAS. Systemically absorbed 2BE was rapidly cleared from blood (t1/2-RAT < 10 min; t1/2-MOUSE < 5 min after the 1-day exposure) independent of exposure concentration. Proportional increases in AUC2BE relative to increases in exposure concentration indicated linear 2BE kinetics. In contrast, the rate of 2BAA elimination from blood decreased as the exposure concentration increased. Nonproportional increases in AUC2BAA also indicated that 2BAA is eliminated following dose-dependent, nonlinear kinetics. Overall, mice eliminated both 2BE and 2BAA from blood faster than rats. Sex-related differences in 2BAA elimination were most significant with rats, in that females were less efficient in clearing 2BAA from the blood. Differences in renal excretion of 2BAA are possibly responsible for the sex-related difference in the 2BAA blood profiles in rats. As exposure continued, the rates of elimination for both 2BE and 2BAA decreased in both species, resulting in longer residence times in the blood. When 19-month-old naive mice were exposed to 125 ppm, 2BE was rapidly cleared from the systemic circulation, exhibiting clearance profiles similar to young mice. However, old mice eliminated 2BAA from blood > 10 times slower than young mice after 1-day of exposure. This delayed elimination of 2BAA in old mice was less obvious after 3 weeks of exposure, suggesting that there might be other factors in addition to the age of animals that could influence the apparent difference in 2BAA kinetics between old and young mice. It was concluded that the elimination kinetics of 2BE and 2BAA following repeated 2BE exposure appear to be dependent on species, sex, age, time of exposure, as well as the exposure concentration.

Toxicity of furfuryl alcohol to F344 rats and B6C3F1 mice exposed by inhalation.

Groups of F344 rats and B6C3F1 mice were exposed to furfuryl alcohol vapor for 6 hours per day, 5 days per week for 14 days (0, 16, 31, 63, 125, 250 ppm) or 13 weeks (0, 2, 4, 8, 16, 32 ppm). Reduced survival was observed in the 14-day study at 250 ppm. Final mean body weights of rats and mice exposed to 125 ppm and of female mice exposed to 63 ppm were lower than controls at the end of the 14-day study; there were no significant differences in mean body weight among chemical-exposed and control groups in the 13-week study. Exposure to furfuryl alcohol had no toxicologically significant effect on organ weights in either rats or mice, and did not cause any adverse changes in hematology or serum chemistry parameters evaluated in rates in the 13-week study. Microscopic lesions associated with exposure to furfuryl alcohol were present in the nose of both rats and mice at all exposure concentrations in both the 14-day and 13-week studies. Lesions observed in the 14-day study consisted of inflammation of the nasal turbinates accompanied by necrosis and squamous metaplasia of the respiratory epithelium and necrosis and degeneration of the olfactory epithelium. Similar lesions were observed in both rats and mice in the 13-week study. In addition, squamous metaplasia and goblet cell hyperplasia of the respiratory epithelium, squamous metaplasia of the transitional epithelium and degeneration, hyperplasia and some respiratory metaplasia of the olfactory epithelium were also observed in rats in the 13-week study, and hyaline droplets in the respiratory epithelium and chronic inflammation and respiratory metaplasia in the olfactory epithelium were observed in mice in the 13-week study. In general the nasal passages of mice appeared less sensitive than those of rats at the concentrations used in the 13-week study; a no-observable-effect level was not achieved in either the 14-day or the 13-week study.

Inhalation toxicity and carcinogenicity of isoprene in rats and mice: comparisons with 1,3-butadiene.

As with 1,3-butadiene (BD), inhalation exposure of B6C3F1 mice to isoprene (2-methyl-1,3-butadiene) caused a macrocytic anemia; induced increases in sister chromatid exchanges in bone marrow cells and in levels of micronucleated erythrocytes in peripheral blood; and produced degeneration of the olfactory epithelium, forestomach epithelial hyperplasia, and testicular atrophy. Most notable was the finding that like BD, isoprene induced neoplasms in the liver, lung, Harderian gland, and forestomach of mice. The carcinogenic effects of isoprene were observed after a 26-week exposure (6 h/day, 5 days/week) of male mice to 700 ppm or higher concentrations of isoprene followed by a 26-week recovery period. Unlike BD, isoprene did not induce lymphomas or hemangiosarcomas of the heart in mice under these conditions nor did it induce chromosomal aberrations in mouse bone marrow cells. No toxicological effects were evident in rats exposed for 13 weeks to either isoprene or BD at concentrations up to 7000 ppm or 8000 ppm, respectively. Interstitial cell hyperplasia of the testis was observed in male F344 rats exposed to 7000 ppm isoprene for 26 weeks, and following a 26-week recovery period, there was a marginal increase in benign testicular interstitial cell tumors.

Two-year and lifetime toxicity and carcinogenicity studies of ozone in B6C3F1 mice.

To evaluate the toxicity and carcinogenic potential of long-term exposure to ozone, B6C3F1 mice were exposed by whole-body inhalation to 0, 0.12, 0.5, or 1.0 ppm and 0, 0.5, or 1.0 ppm ozone for 24 or 30 mo (lifetime), respectively. The incidence of alveolar/ bronchiolar adenomas and carcinomas (combined) increased (p < 0.05) in female mice exposed to 1.0 ppm for 24 or 30 mo and marginally increased (p > 0.05) in male mice exposed to concentrations of 0.5 or 1.0 ppm. An increased incidence of nonneoplastic lesions were observed in the nasal cavities and in the centriacinar region of the lung of mice exposed to 0.5 or 1.0 ppm for 24 and 30 mo. Nasal cavity lesions were mild and included hyaline degeneration, hyperplasia, squamous metaplasia, fibrosis and suppurative inflammation of the transitional and respiratory epithelium of the lateral wall, and atrophy of the olfactory epithelium. Lung lesions included replacement of the epithelium of the alveolar ducts and adjacent alveolar septa with epithelium similar to that normally found in terminal bronchioles (metaplasia) and associated alveolar histiocytosis. Based on the results of these studies, we conclude that inhalation exposure of B6C3F1 mice to ozone for 24 or 30 mo (a) is carcinogenic in female B6C3F1 mice exposed to 1.0 ppm of ozone based on an increased incidence of alveolar/bronchiolar adenoma or carcinoma and (b) results in mild, site-specific, nonneoplastic lesions in the nasal cavity and centriacinar lung of male and female mice exposed to 0.5 or 1.0 ppm of ozone for 2 yrs, which persist with continued exposure to 30 mo. It is uncertain whether or not the marginal increase (p > 0.05) of alveolar/bronchiolar neoplasms in male B6C3F1 mice resulted from exposure to ozone.

Toxicity of inhaled chloroprene (2-chloro-1,3-butadiene) in F344 rats and B6C3F(1) mice.

Chloroprene (2-chloro-1,3-butadiene) is a high production chemical used almost exclusively in the production of polychloroprene (neoprene) elastomer. Because of its structural similarity to isoprene (2-methyl-1,3-butadiene) and to 1,3-butadiene, a potent trans-species carcinogen, inhalation studies were performed on chloroprene to characterize its toxicological potential and to provide a basis for selecting exposure concentrations for chronic toxicity and carcinogenicity studies. Thirteen-week inhalation toxicology studies were conducted in male and female F344 rats and B6C3F(1) mice at exposure concentrations of 0, 5, 12, 32 or 80 ppm (6 h/day; 5 days/week). A 200 ppm exposure group was also included for rats only, because a previous study showed that this concentration of chloroprene is lethal to mice. In mice, exposure to 80 ppm chloroprene caused a marginal decrease in body weight gain in males and epithelial hyperplasia of the forestomach in males and females. This lesion has been observed in mice exposed to isoprene or 1,3-butadiene. In rats, exposure to 80 ppm chloroprene or higher concentrations caused degeneration and metaplasia of the olfactory epithelium and exposure to 200 ppm caused anemia, hepatocellular necrosis and reduced sperm motility. These lesions have not been observed in rats exposed to isoprene or 1,3-butadiene. The profile of toxic effects of chloroprene is considerably different from that of isoprene or 1,3-butadiene; this may be due to differences in exposure concentrations that were used in toxicology studies of these compounds and /or to the influence of the chlorine substitution on the toxicokinetics of these compounds, on their biotransformation, or on the reactivity of metabolic intermediates with tissue macromolecules.

Thirteen-week inhalation toxicity of 2- and 4-chloronitrobenzene in F344/N rats and B6C3F1 mice.

Toxicity studies were performed by exposing F344/N rats and B6C3F1 mice to 2- and 4-chloronitrobenzene (CNB) by whole-body inhalation 6 hr/day, 5 days/week, for 13 weeks. Animals were evaluated for clinical chemistry (rats), hematology (rats), histopathology, and body/organ weights. Exposure concentrations were 0, 1.1, 2.3, 4.5, 9, and 18 ppm for 2-CNB and 0, 1.5, 3, 6, 12, and 24 ppm for 4-CNB. All rats in the 2-CNB study survived until the end of the study. Two male mice in the 18-ppm group in the 2-CNB study, however, died during Week 12; no deaths attributable to 4-CNB exposure occurred in rats or mice. In both studies, the mean body weight gains of exposed animals were similar to those of the respective controls. In rats, inhalation exposure to 2- or 4-CNB resulted in methemoglobinemia leading to a regenerative anemia and a variety of tissue changes secondary to the oxidative erythrocyte injury. In the 2-CNB study, methemoglobinemia resulted in a normocytic, normochromic, responsive anemia, whereas with 4-CNB, the methemoglobinemia was more severe and resulted in a macrocytic, hyperchromic, responsive anemia. Alterations of erythrocyte morphology were observed in both studies; changes included Heinz bodies, poikilocytes, and polychromasia. In rats, both isomers caused increases in serum activities of alanine aminotransferase and sorbitol dehydrogenase and increased bile acid concentrations. Microscopic liver changes included hemosiderin deposition in Kupffer cells (rats and mice exposed to 4-CNB), hepatocytomegaly (mice), and cytoplasmic basophilia (rats). Hepatocellular necrosis and chronic inflammation observed in mice were rather specific to the 2-CNB isomer, as only slight evidence of focal necrosis in the liver was observed in mice exposed to 4-CNB. Splenic lesions included hemosiderin accumulation capsular fibrosis, and increased hematopoietic cell proliferation. Increased bone marrow hemosiderin and hematopoietic cell proliferation and kidney tubule hemosiderin deposition were also observed. Other findings, attributed to chemical exposure but not to the hematotoxicity, were described. Lesions included hyaline droplet nephropathy and degeneration of the testis in male rats exposed to 4-CNB, inflammation of the harderian gland in rats exposed to 4-CNB, hyperplasia of the nasal cavity epithelium in rats exposed to 2-CNB, and hyperplasia of the forestomach epithelium in mice exposed to 4-CNB; these lesions have not been described previously in studies with these chemicals. Based on the exposure concentrations evaluated, A no-observed-adverse-effect level (NOAEL) for histopathological injury in mice was 4.5 ppm for 2-chloronitrobenzene and 6 ppm for 4-chloronitrobenzene; a NOAEL was not determined for rats.

Isoprene, an endogenous hydrocarbon and industrial chemical, induces multiple organ neoplasia in rodents after 26 weeks of inhalation exposure.

Isoprene, the 2-methyl analogue of 1,3-butadiene, is a high production chemical used largely in the manufacture of synthetic rubber and is the major endogenous hydrocarbon exhaled in human breath. Thirteen-week inhalation toxicology studies of isoprene were conducted in male and female F344 rats and B6C3F1 mice at exposure concentrations of 0, 70, 220, 700, 2200, and 7000 ppm (6 h/day; 5 days/week). In addition, 26-week inhalation studies at the same exposure levels, followed by a 26-week recovery period, were conducted in male rats and mice. The 13-week exposures produced no discernible exposure-related toxic effects in rats. Interstitial cell hyperplasia of the testis was observed in all male rats in the 7000 ppm group after 26 weeks of exposure; following the 26-week recovery period the only effect in rats was a marginal increase in benign testicular interstitial cell tumors. In mice, isoprene induced toxic and carcinogenic effects at multiple organ sites. Following the 26-week exposure and 26-week recovery periods, incidences of neoplastic lesions in the liver, lung, forestomach, and harderian gland were significantly increased. Neoplastic effects were observed at 700 ppm and higher exposures. Non-neoplastic lesions in mice exposed to isoprene included spinal cord degeneration, testicular atrophy, degeneration of the olfactory epithelium, and epithelial hyperplasia of the forestomach. A partial hindlimb paralysis and a nonresponsive macrocytic anemia were also seen in mice. Most of the toxic and carcinogenic effects caused by isoprene, as well as the species' difference in response, had been observed after inhalation exposures to 1,3-butadiene.

Toxicology and carcinogenesis studies of ozone and ozone 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone in Fischer-344/N rats.

The purpose of this study was to evaluate the toxicity and potential carcinogenicity or cocarcinogenicity of ozone exposure in rats. Fischer-344/N (F-344/N) rats were exposed 6 hr/day, 5 days/wk, to 0, 0.12, 0.5, or 1.0 ppm ozone by inhalation for 2-yr and lifetime exposures. The cocarcinogenicity study included subcutaneous administration of 0, 0.1, or 1.0 mg/kg body weight of 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK) and inhalation of 0 or 0.5 ppm ozone to male rats. NNK was administered by subcutaneous injections 3 times per week for the first 20 wk with ozone inhalation exposure. The ozone inhalation exposure was for 2 yr (104 wk), including the first 20 wk of NNK treatment and continuing for 84 wk after the last NNK injection. Ozone exposure caused a concentration-related increase in inflammation of the centriacinar region of the lung. There was also increased fibrosis and an extension of the bronchiolar epithelium in these centriacinar regions to involve the proximal alveoli. There was no increased incidence of neoplasms at any site, including the lung, that was associated with ozone exposure. Rats administered 1.0 mg/kg body weight NNK alone had an increased incidence of bronchiolar/alveolar neoplasms, but this effect was not enhanced by ozone exposure. Ozone exposure for 2 yr and lifetime was associated with site-specific toxic alterations in the nasal passage and lung similar to those previously described for short-term exposures. While there was significant attenuation of the pulmonary lesions as compared to short-term exposures, lesions persisted in the lifetime study and there was evidence of a mild progressive fibrosis. We conclude that under the conditions of these studies: (a) ozone exposure is not carcinogenic to either male or female F-344/N rats, (b) ozone does not enhance the incidence of pulmonary neoplasms in F-344/N rats exposed to a known pulmonary carcinogen (NNK), and (c) mild site-specific toxic lesions characteristic of ozone exposure persist in the nasal passage and lung throughout the lifetime of the rat with continued ozone exposure.

Carcinogenicity of 1,3-butadiene in C57BL/6 x C3H F1 mice at low exposure concentrations.

The carcinogenicity of inhaled 1,3-butadiene was evaluated in C57BL/6 x C3H F1 mice exposed to concentrations of this gas ranging from 6.25 to 625 ppm. Butadiene is a high production volume chemical, used mainly in the manufacture of synthetic rubber. In these 2-yr inhalation studies, a potent multisite carcinogenic response was observed, including neoplasms of the lung at concentrations as low as 6.25 ppm. Early occurrence and extensive development of lethal lymphocytic lymphomas in mice exposed to 625 ppm of butadiene reduced the number of animals at risk for the expression of later developing neoplasms at other sites; at lower exposure concentrations, dose responses were demonstrated for hemangiosarcomas of the heart and neoplasms of the lung, forestomach, Harderian gland, preputial gland, liver, mammary gland, and ovary. So far, no long-term studies on butadiene have been conducted at exposure concentrations that have not shown a carcinogenic response. In separate experiments with reduced exposure durations, butadiene induced neoplastic responses at multiple organ sites even after only 13 wk of exposure. Because of the correspondence between these animal data and recent epidemiology findings, there is a worldwide public health need to reevaluate current workplace exposure standards for 1,3-butadiene.

Inhalation toxicity studies of cobalt sulfate in F344/N rats and B6C3F1 mice.

Groups of 10 F344/N rats and B6C3F1 mice of each sex were exposed to cobalt sulfate heptahydrate aerosols of 0, 0.3, 1.0, 3.0, 10, or 30 mg/m3, 6 hr per day, 5 days per week, for 13 weeks. All rats and female mice and all but 2/10 male mice exposed at the top concentration survived to the end of the studies. Polycythemia was observed in exposed rats but not in mice. Sperm motility was decreased in mice exposed at 3 mg/m3 (the lowest concentration evaluated) and at higher concentrations, and increased numbers of abnormal sperm and decreased testis and epididymal weights occurred in mice exposed to 30 mg/m3. Cobalt content in the urine of rats increased with increasing atmospheric cobalt exposure. Primary histopathologic effects were limited to the respiratory tract. Lesions in rats and mice included degeneration of the olfactory epithelium, squamous metaplasia of the respiratory epithelium, and inflammation in the nose; inflammation, necrosis, squamous metaplasia, ulcers (rats), and inflammatory polyps (rats) of the larynx; metaplasia of the trachea (mice); and fibrosis, histiocytic infiltrates, bronchiolar epithelial regeneration, and epithelial hyperplasia in the alveoli of the lung. The most sensitive tissue was the larynx, with squamous metaplasia observed in rats and mice at the lowest exposure concentration of 0.3 mg/m3. Thus, a no-observed-adverse-effect level was not reached in these studies.

Inhalation toxicology and carcinogenicity of 1,3-butadiene in B6C3F1 mice following 65 weeks of exposure.

1,3-Butadiene, a large-production volume chemical used mainly in the manufacture of synthetic rubber, was found to induce multiple-organ carcinogenicity in male and female B6C3F1 mice at exposure concentrations (625 and 1250 ppm) equivalent to and below the OSHA standard of 1000 ppm. Since this study was terminated after 60 weeks of exposure because of reduced survival due to fatal tumors, and because dose-response relationships for 1,3-butadiene-induced neoplastic and nonneoplastic lesions were not clearly established, a second long-term inhalation study of 1,3-butadiene in B6C3F1 mice was conducted at lower exposure concentrations, ranging from 6.25 to 625 ppm. Both the histopathological findings from animals dying through week 65 and the results of evaluations of animals exposed for 40 and 65 weeks are presented in this report. Exposure to 1,3-butadiene caused a regenerative anemia at concentrations of 62.5 ppm and higher. Testicular atrophy was induced at 625 ppm, and ovarian atrophy was observed at 20 ppm and higher. During the first 50 weeks of the study, lymphocytic lymphoma was the major cause of death of mice exposed to 625 ppm 1,3-butadiene. Neoplasms of the heart, forestomach, lung, Harderian gland, mammary gland, ovary, and liver were frequently observed in 1,3-butadiene-exposed mice that died between week 40 and week 65 of the study. Studies in which exposure to 1,3-butadiene was stopped after limited periods were also included to assess the relationship between exposure levels and duration of exposures on the outcome of 1,3-butadiene-induced carcinogenicity. In these studies, lymphocytic lymphomas were induced in male mice exposed to 625 ppm 1,3-butadiene for only 13 weeks. The incidence of lymphocytic lymphoma in male mice exposed to 625 ppm 1,3-butadiene for 26 weeks was two times that in mice exposed to 625 ppm for 13 weeks. However, when the exposure concentration was reduced by half to 312 ppm and the exposure duration extended to 52 weeks, the incidence of lymphocytic lymphoma was reduced by 90%. Thus, the multiple of the exposure concentration times the exposure duration did not predict the incidence of lymphocytic lymphoma in mice. The early mortalities resulting from lymphocytic lymphomas in male mice exposed to 625 ppm 1,3-butadiene limited the expression of tumors at other sites. A clearer dose-response for 1,3-butadiene-induced neoplasia should be apparent from experiments in mice exposed to lower concentrations of this chemical for 2 years.

Inhalation toxicology of isoprene in F344 rats and B6C3F1 mice following two-week exposures.

Isoprene (2-methyl-1,3-butadiene) was selected for toxicologic evaluations because of its structural similarity to 1,3-butadiene, a potent rodent carcinogen. Two-week inhalation toxicology studies of isoprene were conducted in F344 rats and B6C3F1 mice at exposure concentrations of 0, 438, 875, 1750, 3500, or 7000 ppm. For rats, there were no chemically related changes in survival, body weight gain, clinical signs, hematologic or clinical chemistry parameters, or gross or microscopic lesions. Exposure of mice to isoprene did not produce mortalities and only caused a decrease in body weight gain for male mice in the 7000 ppm exposure group; however, hematologic changes and microscopic lesions including testicular atrophy, olfactory epithelial degeneration, and forestomach epithelial hyperplasia were observed in isoprene-exposed mice. Similar toxicologic effects have been previously observed in B6C3F1 mice exposed to 1,3-butadiene. A species difference in susceptibility between rats and mice exposed to isoprene was evident in these short-term exposure studies.

Toxicity studies on lidamidine hydrochloride (WHR-1142A), a novel antidiarrheal agent.

The acute oral LD50 of 1-(2,6-dimethylphenyl)-3-amidinourea hydrochloride (WHR-1142A, lidamidine hyrochloride) was 260 (208, 328) mg/kg in male mice, 267 (212, 336) mg/kg in male rats and 160 (130, 197) mg/kg in female rats. A daily oral dose of 10 mg/kg for 30 days was well tolerated in the rat and monkey. Histologic changes were reversible and for the most part could be explained on the basis of one or more of the several pharmacologic effects of WHR-1142A. A short-lived hyperglycemic effect was a prominent effect in mice and rats. This effect was seen occasionally in high doses in the monkey, suggesting a species difference.