Search

Two-Week, Repeated Inhalation Exposure of F344/N Rats and B6C3F Mice to Ferrocene. SUN, J. D., DAHL, A. R., GILLETT, N. A., BARR, E. B., CREWS, M. L., EIDSON, A. F., BECHTOLD, W. E., BURT, D. G., DIETER, M. P., AND HOBBS, C. H. (1991). . . 17, 150-158. Ferrocene (dicyclopentadienyl iron; CAS No. 102-54-5) is a relatively volatile, organometallic compound used as a chemical intermediate, a catalyst, and as an antiknock additive in gasoline. It is of particular interest because of its structural similarities to other metallocenes that have been shown to be carcinogenic. F344/N rats and B6C3F, mice were exposed to 0, 2.5, 5.0, 10, 20, and 40 mg ferrocene vapor/m3, 6 hr/day for 2 weeks. During these exposures, there were no mortality and no observable clinical signs of ferrocene-related toxicity in any of the animals. At the end of the exposures, male rats exposed to the highest level of ferrocene had decreased body-weight gains relative to the weight gained by filtered air-exposed control rats, while body-weight gains for all groups of both ferrocene- and filtered air-exposed female rats were similar. Male mice exposed to the highest level of ferrocene also had decreased body-weight gains, relative to controls, while female mice had relative decreases in body-weight gains at the three highest exposure levels. Male rats had a slight decrease in relative liver weight at the highest level of exposure, whereas no relative differences in organ weights were seen in female rats. Male mice had exposure-relative decreases in liver and spleen weights, and an increase in thymus weights, relative to controls. For female mice, relative decreases in organ weights were seen for brain, liver, and spleen. No exposure-related gross lesions were seen in any of the rats or mice at necropsy. Histopathological examination was done only on the nasal turbinates, lungs, liver, and spleen. The only exposure-related finding was histopathologic lesions in the nasal turbinates of both species. These lesions were primarily centered in the olfactory epithelium and were morphologically diagnosed as subacute, necrotizing inflammation. Nasal lesions were observed in all ferrocene-exposed animals and differed only in severity, which was dependent on the exposure concentration. In vitro metabolism studies of ferrocene showed that nasal tissue, particularly the olfactory epithelium, had 10 times higher “ferrocene hydroxylating” activity than did liver tissue from the same animals. These results suggest that the mechanism of ferrocene toxicity may be the intracellular release of ferrous ion through ferrocene metabolism, followed by iron-catalyzed lipid peroxidalion of cellular membranes. [ABSTRACT FROM PUBLISHER]

Effect of Inhaled Azodicarbonamide on F344/N Rats and B6C3F, Mice with 2-Week and 13-Week Inhalation Exposures. MEDINSKY, M. A., BECHTOLD, W. E., BIRNBAUM, L. S., BOND, J. A., BURT, D. G., CHENG, Y. S., GILLFTT, N. A., GULATI, D. K., HOBBS, C. H., AND PICK-RELL, J. A. (1990). Fundam. Appl. Toxicol 15, 308/319. Azodicarbonamide (ADA), a compound used in the baking and plastics industries, has been reported to cause pulmonary sensiti-zation and dermatitis in people. Two-week repeated and 13-week subchronic inhalation exposures of F344/N rats and B6C3F, mice to ADA were conducted to determine the toxicity of inhaled ADA. The mean air concentrations of ADA in the 2-week studies were 207, 102, 52, 9.4, or 2.0 mg/m3. No exposure-related mortality nor abnormal clinical signs were observed in rats or mice during or after exposure. The terminal body weights were slightly depressed in the highest exposure group. Liver weights were lower in male rats exposed to 200 mg ADA/m3. No significant lesions were noted on either gross or histologic evaluation of rats or mice. In the 13-week subchronic study, the mean air concentrations of ADA were 204, 100, or 50 mg/m3. No mortality or clinical signs related to exposure were observed. The terminal body weights of exposed rats were not significantly different from those of control rats but were significantly depressed in mice exposed to 100 or 200 mg ADA/m3. No histopathological lesions were noted in mice. Lung weights were increased and enlarged mediastinal and/or tracheobronchial lymph nodes were noted in rats exposed to 50 mg ADA/m3. No exposure-related lesions were observed microscopically in rats exposed to 100 or 200 mg ADA/m3. All rats in the 50 mg ADA/m3 exposure group only had lung lesions that consisted of perivascular cuffing with lymphocytes and a multifocal type II cell hyperplasia, suggesting a possible immune reaction to an antigen in the lung. Viral titers for rats exposed to 50 mg ADA/m3 were negative for Sendai virus and pneumonia virus of mice, which produce similar lesions. The possibility of an unknown viral antigen causing this lesion cannot be eliminated. Lung tissue from male rats was analyzed for ADA and biurea, the major metabolite of ADA. No ADA was detected. The amount of biurea in the lungs increased nonlinearly with increasing exposure concentration, suggesting that clearance was somewhat impaired with repeated exposures. However, even at the highest exposure concentration, this amount of biurea was less than 1 % of the estimated total ADA deposited over the exposure period. In summary, ADA is rapidly cleared from the lungs, even when inhaled at concentrations up to 200 mg/m3. Exposure to ADA for up to 13 weeks did not appear to be toxic to rodents [ABSTRACT FROM PUBLISHER]

The Fate of Inhaled Azodicarbonamide in Rats. Mewhinney, J. A., AYRES, P. H., BECHTOLD, W. E., DUTCHER, J. S., CHENG, Y. S., BOND, J. A., MEDINSKY, M. A., HENDERSON, R. F., AND BIRNBAUM, L. S. (1987). . , 372–381. Azodicarbonamide (ADA) is widely used as a blowing agent in the manufacture of expanded foam plastics, as an aging and bleaching agent in flour, and as a bread dough conditioner. Human exposures have been reported during manufacture as well as during use. Groups of male F344/N rats were administered ADA by gavage, by intratracheal instillation, and by inhalation exposure to determine the disposition and modes of excretion of ADA and its metabolites. At 72 hr following gavage, 30% of the administered ADA was absorbed whereas following intratracheal instillation, absorption was 90%. Comparison between groups of rats exposed by inhalation to ADA to achieve body burdens of 24 or 1230 μg showed no significant differences in modes or rates of excretion of [C]ADA equivalents. ADA was readily converted to biurea under physiological conditions and biurea was the only C-labeled compound present in excreta. [C]ADA equivalents were present in all examined tissues immediately after inhalation exposure, and clearance half-times on the order of 1 day were evident for all tissues investigated. Storage depots for [C]ADA equivalents were not observed. The rate of buildup of [C]ADA equivalents in blood was linearly related to the lung content as measured from rats withdrawn at selected times during a 6-hr inhalation exposure at an aerosol concentration of 25 μg, ADA/liter. In a study extending 102 days after exposure, retention of [C]ADA equivalents in tissues was described by a two-component negative exponential function. The results from this study indicate that upon inhalation, ADA is rapidly converted to biurea and that biurea is then eliminated rapidly from all tissues with the majority of the elimination via the urine. [ABSTRACT FROM PUBLISHER]

Butadiene diepoxide (BDO2), a metabolite of 1,3-butadiene (BD) and potent mutagen, is suspected to be a proximate carcinogen in the multisite tumorigenesis in B6C3F1 mice exposed to BD. Rats, in contrast to mice, do not form much BDO2 when exposed to BD, and they do not form cancers after exposure to the low levels of BD at which mice develop lung and heart tumors. Tests were planned to determine the direct carcinogenic potential of BDO2 in similarly exposed rats and mice, to see if they would develop tumors of the lung (the most sensitive target organ in BD-exposed mice) or other target tissues. The objective of the current series of studies was to assess the acute toxicity and dosimetry to blood and lung of BDO2 administered by various routes to B6C3F1 mice and Sprague-Dawley rats. The studies were needed to aid in the design of the carcinogenesis study. Initial studies using intraperitoneal injection of BDO2 were designed to determine the rate at which each of the species cleared the compound from the body; the clearance was equally fast in both species. A second study was designed to determine if the highly reactive BDO2, when deposited in the lung, would enter the bloodstream from the lung; intratracheally instilled BDO2 did enter the bloodstream, indicating that exposure via the lungs would result in BDO2 reaching other organs of the body. In a third study, rats and mice were exposed by inhalation for 6 h to 12 ppm BDO2 to determine blood and lung levels of the compound. Concentrations of BDO2 in the lung immediately after the exposure were 2 to 3 times higher than in the blood in both species (approximately 500 and 1000 pmol/g blood in the rat and mouse, respectively). As expected, mice received a higher dose/g tissue than did rats, consistent with the higher minute volume/kg body weight of the mice. The inhalation dosimetry study was followed by a histopathology study to determine the acute toxicity to rodents following a single, 6-h exposure to 18 ppm BDO2. No clinical signs of toxicity were observed; lesions were confined to the olfactory epithelium where areas of necrosis were observed. Analysis of bronchoalveolar lavage fluid did not indicate pulmonary inflammation. Based on these findings, an attempt was made to expose rats and mice repeatedly (for 7 days) to 10 and 20 ppm BDO2, but these exposure concentrations proved too toxic, due to inflammation of the nasal mucosa and occlusion of the nasal airway, a lesion that cannot be tolerated by obligate nose breathers. Finally, the toxicity of rats and mice exposed 6 h/day for 5 days to 0. 2.5, or 5.0 ppm BDO2 was determined. The repeated exposures caused no clinical signs of toxicity, nor were any lesions observed in the respiratory tract or other major organs. Therefore, the final design selected for the carcinogenesis study comprised exposing the rats and mice for 6 h/day, 5 days/week for 6 weeks to 0, 2.5, or 5.0 ppm BDO2. [ABSTRACT FROM PUBLISHER]

Benzene is a ubiquitous environmental pollutant that is known to cause hematotoxicity and leukemia in humans. The initial oxidative metabolite of benzene has long been suspected to be benzene oxide (3,5-cyclohexadiene-1,2-oxide). During in vitro experiments designed to characterize the oxidative metabolism of [14C]benzene, a metabolite was detected by HPLC-radioactivity analysis that did not elute with other known oxidative metabolites. The purpose of our investigation was to prove the hypothesis that this metabolite was benzene oxide. Benzene (1 mM) was incubated with liver microsomes from human donors, male B6C3F1 mice, or male Fischer-344 rats, NADH (1 mM), and NADPH (1 mM) in 0.1 M sodium phosphate buffer (pH 7.4) and then extracted with methylene chloride. Gas chromatography-mass spectrometry analysis of incubation extracts for mice, rats, and humans detected a metabolite whose elution time and mass spectrum matched that of synthetic benzene oxide. The elution time of the benzene oxide peak was approximately 4.1 min, while phenol eluted at approximately 8 min. Benzene oxide also coeluted with the HPLC peak of the previously unidentified metabolite. Based on the 14C activity of this peak, the concentration of benzene oxide was determined to be approximately 18 microM, or 7% of total benzene metabolites, after 18 min of incubation of mouse microsomes with 1 mM benzene. The metabolite was not observed in incubations using heat-inactivated microsomes. This is the first demonstration that benzene oxide is a product of hepatic benzene metabolism in vitro. The level of benzene oxide detected suggests that benzene oxide is sufficiently stable to reach significant levels in the blood of mice, rats, and humans and may be translocated to the bone marrow. Therefore benzene oxide should not be excluded as a possible metabolite involved in benzene-induced leukemogenesis. [ABSTRACT FROM PUBLISHER]

Effect of Dose on the Disposition of 2-Ethoxyethanol after Inhalation by F344/N Rats. KENNEDY, C. H., BECHTOLD, W. E., CHANG, I-Y., AND HENDERSON, R. F. (1993). . 21, 486–491. Glycol ethers such as 2-ethoxyethanol (EE) are widely used as solvents because they are miscible in aqueous and organic solutions. Toxic effects of EE in rodents include teratogenicity, fetotoxicity, hematotoxicity, and testicular atrophy. The purpose of this study was to determine the effect of dose on the absorption, metabolism, and excretion of 2-ethoxy [U-C]ethanol by F344/N rats after inhalation exposure. Rats were exposed to either 5 ppm EE for 5 hr 40 min or 46 ppm EE for 6 hr. The uptake and metabolism of EE were linear in the concentration range studied. Significant percentages of the retained doses were exhaled during (22%) and after exposure (16%) as CO. Forty-six percent of the retained dose was excreted in the urine. Approximately 10% of the retained dose was detected in the carcass 66 hr after exposure. The major urinary metabolite was ethoxyacetic acid (EAA), the toxic metabolite of EE. The amount of EAA excreted was linearly related to exposure concentration. Ethylene glycol and -ethoxyacetyl glycinate were identified as minor metabolites excreted in the urine. The results of this study suggest that the toxicity of inhaled EE should be directly proportional to the exposure concentration up to 46 ppm if the toxicity Of EE is due to EAA. [ABSTRACT FROM PUBLISHER]

Uptake of Vinylidene Fluoride in Rats Simulated by a Physiological Model. Medinsky, M. A., Bechtold, W. E., Birnbaum, L. S., Chico, D. M., Gerlach, R. F., and Henderson, R. F. (1988). 11, 250–260. The purpose of this study was to develop a physiological model to simulate the uptake of vinylidene fluoride (VDF), an important plastics monomer, in laboratory animals. Male Fischer 344/N rats were exposed nose-only for 6 hr to concentrations of VDF ranging from 27 to 16,000 ppm. Tidal volume (mean, 1.51 ml/breath) and respiratory frequency (mean, 132 breaths/min) were not influenced by exposure concentration. Experimentally determined, steady-state blood levels of VDF, obtained by gas chromatog-raphy-head space analysis of samples from rats with indwelling jugular cannulas, increased linearly with increasing exposure concentration up to 16,000 ppm. VDF tissue/air partition coefficients were determined experimentally to be 0.07,0.18,0.8, 1.0, and 0.29 for water, blood, liver, fat, and muscle, respectively. These values and calculated constants for total body elimination of VDF, and were incorporated into the physiological model. Model predictions agreed with the experimentally determined data. Time to reach steady-state blood levels of VDF was less than 15 min for all concentrations. After cessation of exposure, blood levels of VDF decreased to 10% of steady-state levels by 1 hr. Simulation of the metabolism of VDF indicated that although blood levels of VDF increased linearly with increasing concentration the amount of VDF metabolized per 6-hr exposure period approached a maximum at about 2000 ppm VDF. [ABSTRACT FROM PUBLISHER]

Excretion and Metabolism of 1-Nitropyrene in Rats after Oral or Intraperitoneal Administration. DUTCHER, J. S., SUN, J. D., BECHTOLD, W. E., and UKEFER, C. J. (1985). . 5, 287–296. Many nitro-substituted polycyclic aromatic hydrocarbons (NPAHs) have been identified as environmental pollutants and have been found to be mutagens and carcinogens in bacteria and mammalian systems. They require metabolism to express their biological activity. The metabolism and excretion of 1-nitropyrene (NP), a prevalent NPAH, by Fischer-344 rats after intraperitoneal (ip) or oral administration was studied. Radiolabeled NP was administered to rats (10 mg NP/kg body wt), and urine and feces were collected for 7 days. After ip administration of [C]NP, 60% of the radioactivity was found in the urine and 20% in the feces. Likewise, 55 and 35% of the orally administered C was found in urine and feces, respectively. Both urine and feces were analyzed by high-pressure liquid chromatography for metabolites. The majority of the radioactivity in both urine and feces was associated with very polar metabolites, none accounting for more than 10% of the dose. Small amounts (less than 1% of the dose) of aminopyrene (AP), acetylaminopyrene, and NP were detected. A urinary metabolite (3–8% of the dose) was found that converted to acetylaminopyrene phenol (two isomers) when urine was heated overnight at 37°C at pH 4.5. More of this metabolite (2.2 times) as well as AP (1.8 times), was excreted after oral than after ip administration of NP. The NP metabolites found in this study demonstrate that reduction of the nitro group is a significant route of NP metabolism in rats. Since nitroreduction appears to be necessary in the activation of NPAHs to bacterial mutagens, this indicates that similar metabolic pathways are present in rats (catalyzed by mammalian and/or gut bacterial enzymes) and that activation of NPAHs to carcinogens or toxins by nitroreduction is possible. [ABSTRACT FROM PUBLISHER]

Chemical and Biological Properties of Diesel Exhaust Particles Collected during Selected Segments of a Simulated Driving Cycle. BECHTOLD, W. E., DUTCHER, J. S., MOKLER, B. V., LOPEZ, J. A., WOLF, I., LI, A. P., HENDERSON, T. R., AND MCCLELLAN, R. O. (1984). . 4, 370–377. Particle emissions, percentage of organic extractable materials, and mutagenicities of extracts from a diesel engine operating on a test stand have been determined for the full Federal Test Procedure driving cycle and several individual segments thereof. Particle samples were collected using a computer controlled high volume sampler. Extracts of the exhaust particles were screened for the potent mutagens nitropyrene/nitrofluoranthenes by mass spectrometry/mass spectrometry (MS/MS). Results indicate that a long acceleration from 0-55 mph produced approximately seven times more particles per second than the full cycle. Also, the 0-to 55-mph acceleration and a subsequent 55-mph cruise produced significantly higher amounts of mutagens than other segments or the full FTP cycle. A direct correlation of both NO levels and temperature with mutagenicity was noted ( = 0.89 and = 0.89). The specific activities of the extracts showed decreases or remained unchanged when assayed in TA-98 NR or TA-98 1,8 DNP, nitroreductase deficient strains of TA-98. Three extracts were found to have high levels of nitropyrenes/nitrofluoranthenes, and two of the three had high specific activities in TA-98. [ABSTRACT FROM PUBLISHER]