Effect of inhaled residual oil fly ash on the electrocardiogram of dogs

Epidemiology studies have found associations between increases in air pollutants and increases in morbidity and mortality from cardiovascular disease. The 1995 finding by Godleski et al. at Harvard that inhalation exposures of dogs to high concentrations of residual oil fly ash (ROFA) caused changes in the ST segment and T waves in the electrocardiogram (ECG) suggested a potential mechanism, and also suggested that inhaled metals might contribute to the effect. We conducted the present study to establish a baseline correspondence to the Godleski et al. findings in preparation for studies of the cardiac effects of specific particle-borne metals. The ROFA used in this study consisted of 45% carbon and 15.5% transition metals by mass. In vitro assays using cultured A549 cells and rat alveolar macrophages demonstrated that the ROFA was biologically active but was not highly cytotoxic. Four 10.5-yr-old beagles were exposed by oral inhalation to 3 mg/m3 of aerosolized ROFA for 3 h/day on 3 consecutive days. During the exposures, ECGs were continuously recorded from leads I, II, III, and V4. ECG data were also collected during three control exposures to clean air, during one of which changes were induced using drugs as a positive control. The ROFA exposures caused no consistent changes in the amplitude of the ST segment, the form or amplitude of the T wave, or arrhythmias. The data suggested a slight slowing of heart rate during exposure. Whether the difference between the present and previous findings resulted from differences in the composition of the two batches of ROFA or differences in methodology could not be determined by the study. This study did not address the cardiac effects of ROFA in subjects having preexisting cardiac susceptibility factors, nor was it a rigorous evaluation of effects on the frequency distribution of heart rate. Our results indicate that healthy dogs can inhale high concentrations of ROFA without changes in cardiac electrophysiology, which are detectable by clinical evaluations.

Short-term inhalation of particulate transition metals has little effect on the electrocardiograms of dogs having preexisting cardiac abnormalities

There is growing epidemiological evidence for statistical associations between increases in air pollution, especially particulate matter, and increases in cardiovascular morbidity and mortality. Laboratory studies have shown that transition metals contribute strongly to the effects of high lung doses of model particles on changes in the electrocardiograms of animals. The present study evaluated the effects of short-term inhalation exposure to respirable particles of specific oxide and sulfate forms of transition metals on heart rate and the electrocardiogram of old dogs having preexisting cardiac abnormalities. Conscious beagle dogs were exposed by oral inhalation for 3 h on each of 3 successive days to aerosols of manganese, nickel, vanadium, iron, and copper oxides, and nickel and vanadium sulfates as single compounds at concentrations of 0.05 mg/m(3). Electrocardiograms were recorded and evaluated for exposure-related changes in heart rate, heart rate variability, and abnormalities of waveforms. Although the electrocardiograms of this population of dogs having potential age and cardiovascular susceptibility factors reflected their underlying clinical abnormalities, no significant effect of exposure to the transition metal aerosols was observed.

Effects of concurrent ozone exposure on the pathogenesis of cigarette smoke-induced emphysema in B6C3F1 mice

Episodic elevation of air pollutants may exacerbate respiratory distress associated with chronic obstructive pulmonary disease (COPD), yet few experiments have been performed to determine how continuously polluted atmospheres may contribute to the etiology of COPD, in general and pulmonary emphysema in particular. This study describes the effects of concurrent exposure to ozone (O(3)) in the pathogenesis of cigarette smoke (CS)-induced emphysema in the mouse. Female B6C3F1 mice were whole-body exposed either to filtered air (FA) or to mainstream CS at a concentration of 250 mg total particulate material/m(3) for 6 h/day, 5 days/wk for 15 or 32 wk. Concurrently, mice were exposed either to FA or to O(3) at 0.3 ppm for 8 h/night, 5 nights/wk for the same time periods. At necropsy, mouse lungs were lavaged, and bronchoalveolar lavage fluid (BALF) was analyzed for inflammatory cell numbers, total protein, lactate dehydrogenase (LDH) and alkaline phosphatase (AP) activities, superoxide production by isolated alveolar macrophages, glutathione content, inflammatory cytokines, and proteolytic activity. Other lungs were inflated at constant pressure for 6 h with formalin for fixation, routine histopathology, and stereology. After 32 wk of exposure, CS with or without concurrent O(3) exposure produced stereologic evidence of emphysema as previously described. Concurrent O(3) exposure did not worsen any of these parameters, nor did O(3) by itself cause stereologic changes that were consistent with emphysema. The O(3) exposure caused only slight elevations of BALF macrophages, while CS exposure caused marked increases in the numbers of both BALF macrophages and neutrophils. Neutrophils in the BALF in response to CS exposure were also more numerous at 32 wk than at 15 wk. Exposure to CS caused an increase in BALF total protein, LDH, AP, and interleukin (IL)-1beta. After 32 wk, CS exposure was associated with decreased superoxide production from isolated alveolar macrophages. The CS exposure elevated BALF total glutathione primarily at 15 wk. Overall, O(3) had little effect on endpoints that were significantly affected by CS exposure. We conclude that concurrent O(3) exposure has no effect on the induction of emphysema by CS in this animal model.

Effects of subchronic inhalation exposure of rats to emissions from a diesel engine burning soybean oil-derived biodiesel fuel

There is increasing interest in diesel fuels derived from plant oils or animal fats ("biodiesel"), but little information on the toxicity of biodiesel emissions other than bacterial mutagenicity. F344 rats were exposed by inhalation 6 h/day, 5 days/wk for 13 wk to 1 of 3 dilutions of emissions from a diesel engine burning 100% soybean oil-derived fuel, or to clean air as controls. Whole emissions were diluted to nominal NO(x) concentrations of 5, 25, or 50 ppm, corresponding to approximately 0.04, 0.2, and 0.5 mg particles/m(3), respectively. Biologically significant, exposure-related effects were limited to the lung, were greater in females than in males, and were observed primarily at the highest exposure level. There was a dose-related increase in the numbers of alveolar macrophages and the numbers of particles in the macrophages, as expected from repeated exposure, but no neutrophil response even at the highest exposure level. The macrophage response was reduced 28 days after cessation of the exposure. Among the high-level females, the group mean lung weight/body weight ratio was increased, and minimal, multifocal bronchiolar metaplasia of alveolar ducts was observed in 4 of 30 rats. Lung weights were not significantly increased, and metaplasia of the alveolar ducts was not observed in males. An increase in particle-laden macrophages was the only exposure-related finding in lungs at the intermediate and low levels, with fewer macrophages and fewer particles per macrophage at the low level. Alveolar histiocytosis was observed in a few rats in both exposed and control groups. There were statistically significant, but minor and not consistently exposure-related, differences in body weight, nonpulmonary organ weights, serum chemistry, and glial fibrillary acidic protein in the brain. There were no significant exposure-related effects on survival, clinical signs, feed consumption, ocular toxicity, hematology, neurohistology, micronuclei in bone marrow, sister chromatid exchanges in peripheral blood lymphocytes, fertility, reproductive toxicity, or teratology. This study demonstrated modest adverse effects at the highest exposure level, and none other than the expected physiological macrophage response to repeated particle exposure at the intermediate level.

Pulmonary immunity to ragweed in a Beagle dog model of allergic asthma

To create an allergy model in the dog, allergic Beagles with high levels of serum immunoglobulin E (IgE) and eosinophilia were bred; resulting puppies were sensitized to ragweed by intraperitoneal (IP) injection within 24 hours of birth through 22 weeks of age. At least 50% of the puppies developed high levels of serum IgE and eosinophilia. As young adults, 6 of these dogs, and 6 control age-matched, nonallergic, nonimmunized dogs were exposed by inhalation to ragweed twice at 13-day intervals, and a third time 45 days later. Total and ragweed-specific serum IgE and ragweed-specific serum IgG were increased significantly in allergic dogs relative to baseline. Allergic dogs had significantly greater levels of antibody specific for ragweed, as well as higher eosinophil counts in the bronchoalveolar lavage fluid, compared to nonallergic dogs. Airway reactivity to histamine in allergic, but not nonallergic dogs, increased significantly after aerosol exposure to ragweed. After a third exposure to ragweed, airway responses to histamine were elevated in the allergic dogs and remained high for at least 5 months. These results demonstrate the potential of the allergic dog model for investigating the underlying pulmonary immune mechanisms and therapeutic treatment of allergic asthma.

Response of F344 rats to inhalation of subclinical levels of sarin: exploring potential causes of Gulf War illness

Subclinical, repeated exposures of F344 rats to sarin resulted in brain alterations in densities of chlonergic receptor subtypes that may be associated with memory loss and cognitive dysfunction. The exposures also depressed the immune system. The rat appears to be a good model for studying the effects of subclinical exposure to a nerve gas.

MTBE inhaled alone and in combination with gasoline vapor: uptake, distribution, metabolism, and excretion in rats

The purpose of these studies was to extend previous evaluation of methyl tert-butyl ether (MTBE)* tissue distribution, metabolism, and excretion in rats to include concentrations more relevant to human exposure (4 and 40 ppm) and to determine the effects of coinhalation of the volatile fraction of unleaded gasoline on the tissue distribution, metabolism, and excretion of MTBE. Groups of male F344 rats were exposed nose-only for 4 hours to 4, 40, or 400 ppm 14C-MTBE or to 20 or 200 ppm of the light fraction of unleaded gasoline (LFG) containing 4 or 40 ppm 14C-MTBE, respectively. To evaluate the effects of repeated inhalation of LFG on MTBE tissue distribution, metabolism, and excretion, rats were exposed for 4 hours on each of 7 consecutive days to 20 or 200 ppm LFG with MTBE (4 or 40 ppm) followed on the eighth day by a similar exposure to LFG containing 14C-MTBE. Subgroups of rats were evaluated for respiratory parameters, initial body burdens, rates and routes of excretion, and tissue distribution and elimination. The concentrations of MTBE and its chief metabolite, tert-butyl alcohol (TBA), were measured in blood and kidney immediately after exposure, and the major urinary metabolites-2-hydroxyisobutyric acid (IBA) and 2-methyl-1,2-propanediol (2MePD)-were measured in urine. Inhalation of MTBE alone or as a component of LFG had no concentration-dependent effect on respiratory minute volume. The initial body burdens of MTBE equivalents achieved after 4 hours of exposure to MTBE did not increase linearly with exposure concentration. MTBE equivalents rapidly distributed to all tissues examined, with the largest percentages distributed to liver. The observed initial body burden did not increase linearly between 4 and 400 ppm. At 400 ppm, elimination half-times of MTBE equivalents from liver increased and from lung, kidney, and testes decreased compared with the two smaller doses. Furthermore, at 400 ppm the elimination half-time for volatile organic compounds (VOCs) in breath was significantly shorter and the percentage of the initial body burden of MTBE equivalents eliminated as VOCs in breath increased significantly. These changes probably reflect a saturation of blood with MTBE at 400 ppm and strongly suggest that the uptake and fate of MTBE are notably different at exposure concentrations above and below 400 ppm. Single and repeated coexposure to 20 and 200 ppm LFG with MTBE had opposite effects on the total body burden of MTBE equivalents present at the end of exposures compared with those achieved after 4 and 40 ppm MTBE exposures: 20 ppm LFG increased and 200 ppm LFG significantly decreased the burdens of MTBE equivalents present. The effects of coexposure to LFG on blood levels of MTBE equivalents paralleled the effects on body burden. These differences in overall uptake of MTBE equivalents cannot be attributed to alterations of minute volume. The reason for the increase in overall uptake after 20-ppm LFG exposure is not clear. Decreased MTBE absorption (uptake) after single and repeated coexposure to 200 ppm LFG may be due to a decrease in solubility of MTBE in blood caused by inhalation of other hydrocarbons. Investigations on the blood/air partition coefficient of MTBE in the absence and presence of LFG would be needed to confirm this hypothesis. Single and repeated coexposure to either 20 or 200 ppm LFG significantly decreased the percentage of the initial body burden from MTBE equivalents in tissues, including liver, kidney, and testes, immediately and 72 hours after

Particle clearance and histopathology in lungs of C3H/HeJ mice administered beryllium/copper alloy by intratracheal instillation

Beryllium/copper (BeCu) alloys are commonly used in the electronics, automotive, consumer, defense, and aerospace industries. Some individuals exposed occupationally to BeCu alloys have developed chronic beryllium disease. However, little is known of the toxicity and fate of BeCu alloys in the respiratory tract. To begin to address this question, we investigated the pulmonary toxicity and clearance of BeCu alloy (2% Be; 98% Cu) in mice. Groups of 40 female C3H/HeJ mice were administered 12.5, 25, and 100 microg BeCu alloy or 2 and 8 microg Be metal by intratracheal instillation. Mice were sacrificed at 1 h and 1, 7, 14, and 28 days postinstillation. Left lungs were evaluated for histopathological change. Right lungs were analyzed for Be and Cu content. Twenty-five percent of the high-dose BeCu mice and 7.5% of the mid-dose BeCu mice died within 24 h of dosing. Acute pulmonary lesions included acute alveolitis and interstitial inflammation. Type II epithelial cell hyperplasia and centriacinar fibrosis were present by 7 days after dosing. Lesions persisted through 28 days after instillation. No lesions attributable to alloy exposure were present in liver or kidney. Be metal instillation caused no deaths and minimal pulmonary changes over the time studied, indicating that the pulmonary lesions were due to Cu rather than Be. Cu cleared the lung with a half-time of 0. 5-2 days. Be cleared with a half-time of several weeks or longer. Results of this study suggest that exposure to BeCu alloy is more acutely toxic to lung than Be metal. The results of tissue analyses also indicate that, while the Cu component of the alloy clears the lung rapidly, Be is retained and may accumulate upon repeated exposure.

1,3-butadiene: cancer, mutations, and adducts. Part I: Carcinogenicity of 1,2,3,4-diepoxybutane

Reports in the literature suggest that one reason for the greater sensitivity of mice to the carcinogenicity of 1,3-butadiene (BD) is that exposed mice metabolize much more of the BD to 1,2,3,4-diepoxybutane (BDO2) than do exposed rats. The purpose of this study was to determine the tumorigenicity of BDO2 in rats and in mice exposed to the same concentration of the agent. Female B6C3F1 mice and Sprague-Dawley rats, 10 to 11 weeks old, 56 per group, were exposed by inhalation to 0, 2.5, or 5.0 ppm BDO2, 6 hours/day, 5 days/week for 6 weeks. Preliminary dosimetry studies in rodents exposed for 6 hours to 12 ppm BDO2 indicated that blood levels would be expected to be approximately 100 and 200 pmol/g at the two exposure concentrations in the rat and twice those levels in the mouse. During the 6-week exposure, the mice at the high exposure level showed signs of labored breathing during the last week, and four mice died. In the others, however, the respiratory symptoms disappeared after exposure ended. Rats showed no clinical signs of toxicity during exposure but developed labored breathing after the end of the exposure leading to the death of 13 rats within 3 months. At the end of the exposure, some animals (8 per group) were evaluated for the acute toxicity resulting from the BDO2 exposure. The remaining exposed rats and mice were held for 18 months for observation of tumor development. At the end of the exposure, rats had no biologically significant alteration in standard hematological parameters, but mice had a dose-dependent increase in neutrophils and decrease in lymphocytes. In both species the significant histopathologic lesions were in the nose, concentrated around the main airflow pathway. Necrosis, inflammation, and squamous metaplasia of the nasal mucosa, as well as atrophy of the turbinates, were all present at the end of exposure to 5.0 ppm. Within 6 months, necrosis and inflammation subsided, but squamous metaplasia remained in the mice. In rats that died after exposure, squamous metaplasia was seen in areas of earlier inflammation and, in other rats, extended beyond those areas with time. The metaplasia was severe enough to restrict and occlude the nasopharyngeal duct. Later, keratinizing squamous cell carcinomas developed from the metaplastic foci in rats but not mice. At the end of 18 months, the only significant increase in neoplasia in the exposed rats was a dose-dependent increase in neoplasms of the nasal mucosa (0/47, 12/48, and 21/48 for the control, 2.5 ppm, and 5.0 ppm exposures, respectively). Neoplasia of the nasal mucosa did not increase significantly in the mice; neoplastic lesions in the mice were observed in reproductive organs, lymph nodes, bone, liver, Harderian gland, pancreas, and lung. The only significant increase in neoplasms in a single organ in the mice was in the Harderian gland (0/40, 2/42, and 5/36 for the control, 2.5 ppm, and 5.0 ppm exposures, respectively). This tumor accounts for the apparent trend toward an increase in total neoplastic lesions in mice as a function of dose (10/40, 7/42, and 16/36 for control, 2.5 ppm, and 5.0 ppm exposures, respectively). These findings indicate that the metabolite of BD, BDO2, is carcinogenic in the respiratory tract of rats. An increase in respiratory tract tumors was not observed in similarly exposed mice despite the fact that preliminary studies indicated mice should have received twice the dose to tissue compared with the rats. High cytosolic activity of detoxication enzymes in the mouse may account, in part, for the differences in response.

Enhanced pulmonary epithelial replication and axial airway mucosubstance changes in F344 rats exposed short-term to mainstream cigarette smoke

Cigarette smoking is associated with respiratory diseases that may be caused by injury to specific pulmonary cells. The injury may manifest itself as site-specific enhanced cellular replication. In this study, rats were exposed either to mainstream cigarette smoke (CS; 250 mg total particulate matter/m(3)) or to filtered air (FA) for 6 h/day, 5 days/week, for 2 weeks. In one group, cells in S-phase were labeled over 7 days by bromodeoxyuridine (BrdU) released from implanted osmotic pumps (pump labeled), while another group received BrdU by injection 2 h prior to necropsy (pulse labeled). Morphometry showed that the type II epithelial BrdU labeling index (LI) was significantly elevated in the CS-exposed animals of both labeling groups. The axial airway and terminal bronchiolar LIs were enhanced by CS only in the pump-labeled group. In a third group (pulse labeled), 2 weeks of recovery following exposure to CS allowed a normalization in the type II LI. In the pump-labeled rats, the CS-induced elevation of the type II LI was greater than the LI elevation in conducting airways, suggesting that the parenchyma may have been injured more than the conducting airways. The terminal bronchiolar LI in the pump-labeled group, regardless of exposure, was significantly greater than the axial airway LI. Pump labeling, in contrast to pulse labeling, could therefore discern differences among replication rates of conducting airway epithelium in different regions of the lung. Mucosubstance (MS) within the axial airway epithelium was quantified by morphometry. The CS exposure did not increase the total number of MS-containing cells or the total number of axial airway epithelial cells, but there was a phenotype change in the MS cells. Neutral MS cells (periodic acid-Schiff-positive) were significantly decreased, while acid MS cells (alcian blue-positive) were slightly increased by CS exposure. Either cell replication and differentiation or differentiation alone may have changed the phenotype in the MS cell population.

Carcinogenicity of inhaled butadiene diepoxide in female B6C3F1 mice and Sprague-Dawley rats

Previous studies suggest that the greater sensitivity of mice, compared to rats, to the carcinogenicity of 1,3-butadiene (BD) is linked to higher rates of BD metabolism to butadiene diepoxide (BDO2) by mice than rats. The purpose of this study was to determine the tumorigenicity of BDO2 in mice and rats exposed by inhalation to the same concentrations of the agent. Female B6C3F1 mice and Sprague-Dawley rats, 10-11 weeks old, 56/group, were exposed to 0, 2.5, or 5.0 ppm BDO2, 6 h/day, 5 days/week for 6 weeks. At the end of the BDO2 exposure, 8 animals/group were evaluated for toxicity. The remainder of the exposed rats and mice were held for up to 18 months for observation of tumor development. At the end of the exposure, rats had no biologically significant alteration in standard hematological parameters, but mice had a dose-dependent increase in neutrophils and decrease in lymphocytes. Most of the significant lesions in both species were in the nose, concentrated around the main airflow pathway. Necrosis, inflammation, and squamous metaplasia of the nasal mucosa, as well as atrophy of the turbinates, were all present in animals exposed to 5.0 ppm. In mice, necrosis and inflammation subsided within 6 months, but squamous metaplasia remained. In rats that died after exposure, squamous metaplasia was seen in areas of earlier inflammation and extended beyond those areas with time. The metaplasia was severe enough to restrict and occlude the nasopharyngeal duct. Later, keratinizing squamous-cell carcinomas developed from metaplastic foci in rats, but these were not seen in mice. At the end of 18 months, the only significant increase in neoplasia in the exposed rats was a dose-dependent increase in neoplasms of the nasal mucosa (0/47, 12/48, and 21/48 for the control, 2.5 ppm, and 5.0 ppm exposures, respectively). Neoplasia of the nasal mucosa did not increase significantly in the mice. Neoplastic lesions in the mice were observed in reproductive organs, lymph nodes, bone, liver, Harderian gland, pancreas, and lung, but the only significant increase in neoplasms in a single organ in the mice was in the Harderian gland (0/40, 2/42, and 5/36 for the control, 2.5 ppm, and 5.0 ppm exposures, respectively). This tumor accounts for the apparent trend toward an increase in total neoplastic lesions in mice as a function of dose (10/40, 7/42, and 16/36 for control, 2.5 ppm, and 5.0 ppm, respectively). These findings indicate that the metabolite of BD, BDO2, is carcinogenic in the upper respiratory tract of rats. An increase in upper respiratory tract tumors was not observed in similarly exposed mice, despite the fact that preliminary studies indicated mice should have received twice the dose to tissue than did the rats. Higher cytosolic activity of detoxication enzymes has been reported in the liver and lung cells of the mouse compared to the rat, and this may account, in part, for the differences in response. The transport of externally administered BDO2, into the cell and through the cytoplasm, might allow detoxication of the molecule before it reaches critical sites on the DNA. The results indicate that the site of formation of the BDO2 is important for tumor induction.

Cigarette smoke exposure produces more evidence of emphysema in B6C3F1 mice than in F344 rats

Cigarette smoke (CS) causes pulmonary emphysema in humans, but results of previous studies on CS-exposed laboratory animals have been equivocal and have not clearly demonstrated progression of the disease. In this study, morphometry and histopathology were used to assess emphysema in the lungs of B6C3F1 mice and Fischer-344 rats. The animals were exposed, whole-body, to CS at a concentration of 250 mg total particulate matter/m3 for 6 h/day, 5 days/week, for either 7 or 13 months. Morphometry included measurements of parenchymal air space enlargement (alveolar septa mean linear intercept [Lm], volume density of alveolar air space [VVair]), and tissue loss (volume density of alveolar septa [VVspt]). In addition, centriacinar intra-alveolar inflammatory cells were counted to assess species differences in the type of inflammatory response associated with CS exposure. In mice, many of the morphometric parameters indicating emphysema differed significantly between CS-exposed and control animals. In CS-exposed rats, only some of the parameters differed significantly from control values. The Lm in both CS-exposed mice and rats was increased at 7 and 13 months, indicating an enlargement of parenchymal air spaces, but the VVair was increased significantly only in CS-exposed mice. The VVspt was decreased at both time points in mice, but not in rats, indicating damage to the structural integrity of parenchyma. Morphologic evidence of tissue destruction in the mice included alveoli that were irregular in size and shape and alveoli with multiple foci of septal discontinuities and isolated septal fragments. Morphometric differences in the mice at 13 months were greater than at 7 months, suggesting a progression of the disease. Inflammatory lesions within the lungs of mice contained significantly more neutrophils than those lesions in rats. These results suggest that B6C3F1 mice are more susceptible than F344-rats to the induction of emphysema by this CS exposure regimen and that in mice the emphysema may be progressive. Furthermore, the type of inflammatory response may be a determining factor for species differences in susceptibility to emphysema induction by CS exposure.

Dosimetry and acute toxicity of inhaled butadiene diepoxide in rats and mice

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.

Long-lasting effects of chronic ozone exposure on rat nasal epithelium

Ozone, the principal oxidant pollutant in photochemical smog, causes airway epithelial injury in the upper and lower respiratory tract of laboratory animals. We have recently reported that long-term inhalation exposure to ozone causes mucous-cell metaplasia (MCM) in the surface epithelium lining the nasal airways of F344 rats. The principal objective of the present study was to determine the persistence of ozone-induced MCM in the nasal epithelium after the end of a chronic exposure. Male F344/N rats were exposed to 0, 0.25, or 0.5 ppm ozone, for 8 h/d, 7 d/wk for 13 wk. Animals were killed 8 h, 4 wk, or 13 wk after the end of the chronic exposure. Ozone-related alterations in the nasal epithelium were qualitatively and quantitatively characterized through histochemistry, image analysis, and morphometric techniques. Some rats were exposed for an additional 8 h to 0.5 ppm ozone at 13 wk after the end of the chronic exposure to determine whether previous ozone exposure results in persistent changes in the sensitivity of nasal epithelium to acute injury. At the end of the chronic exposure, hyperplasia was present in the nasal epithelium of rats exposed to 0.25 and 0.5 ppm ozone. By 13 wk postexposure, this proliferative alteration was still evident only in the rats exposed to 0.5 ppm ozone. Ozone-induced MCM with associated intraepithelial mucosubstances was evident only in the nasal tissues of rats exposed to 0.5 ppm ozone. Though attenuated, these alterations in the nasal mucous apparatus were still detectable at 13 wk after the end of the exposure. At this same time after the chronic exposure, an acute (8 h) exposure to 0.5 ppm ozone induced an additional increase of mucosubstances in the nasal epithelium of rats previously exposed to 0.5 ppm ozone, but not in rats chronically exposed to 0 or 2.5 ppm ozone. The persistent nature of the ozone-induced MCM in rats documented in this report suggests that ozone exposure may have the potential to induce similar long-lasting alterations in the airways of humans.

Chronic cigarette smoke exposure increases the pulmonary retention and radiation dose of 239Pu inhaled as 239PuO2 by F344 rats

As a portion of a study to examine how chronic cigarette smoke exposure might alter the risk of lung tumors from inhaled 239puO2 in rats, the effects of smoke exposure on alpha-particle lung dosimetry over the life-span of exposed rats were determined. Male and female rats were exposed to inhaled 239PuO2 alone or in combination with cigarette smoke. Animals exposed to filtered air alone served as controls for the smoke exposure. Whole-body exposure to mainstream smoke diluted to concentrations of either 100 or 250 mg total particulate matter m(-3)(LCS or HCS, respectively) began at 6 wk of age and continued for 6 h d(-1), 5d wk(-1), for 30 mo. A single, pernasal, acute exposure to 239PuO2 was given to all rats (control, LCS and HCS) at 12 wk of age. Exposure to cigarette smoke caused decreased body weight gains in a concentration dependent manner. Lung-to-body weight ratios were increased in smoke-exposed rats. Rats exposed to cigarette smoke before the 239PuO2 exposure deposited less 239Pu in the lung than did controls. Except for male rats exposed to LCS, exposure to smoke retarded the clearance of 239Pu from the lung compared to control rats through study termination at 870 d after 239PuO2 exposure. Radiation doses to lungs were calculated by sex and by exposure group for rats on study for at least 360 d using modeled body weight changes, lung-to-body weight ratios, and standard dosimetric calculations. For both sexes, estimated lifetime radiation doses from the time of 239PuO2 exposure to death were 3.8 Gy, 4.4 Gy, or 6.7 Gy for the control, LCS, or HCS exposure groups, respectively. Assuming an approximately linear dose-response relationship between radiation dose and lung neoplasm incidence, approximate increases of 20% or 80% in tumor incidence over controls would be expected in rats exposed to 239PuO2 and LCS or 239PuO2 and HCS, respectively.

Carcinogenic responses of transgenic heterozygous p53 knockout mice to inhaled 239PuO2 or metallic beryllium

The transgenic heterozygous p53+/- knockout mouse has been a model for assessing the tumorigenicity of selected carcinogens administered by noninhalation routes of exposure. The sensitivity of the model for predicting cancer by inhaled chemicals has not been examined. This study addresses this issue by acutely exposing p53+/- mice of both sexes by nose-only inhalation to either air (controls), or to 1 of 2 levels of 239PuO2 (500 or 100 Bq 239Pu) or beryllium (Be) metal (60 or 15 micrograms). Additional wild-type p53+/+ mice were exposed by inhalation to either 500 Bq of 239PuO2 or 60 micrograms of Be metal. These carcinogens were selected because they operate by differing mechanisms and because of their use in other pulmonary carcinogenesis studies in our laboratory. Four or 5 of the 15 mice per sex from each group were sacrificed 6 mo after exposure, and only 2 pulmonary neoplasms were observed. The remainder of the mice were held for life-span observation and euthanasia as they became moribund. Survival of the p53+/- knockout mice was reduced compared to the p53+/+ wild-type mice. No lung neoplasms were observed in p53+/- mice exposed to air alone. Eleven of the p53+/- mice inhaling 239PuO2 developed pulmonary neoplasms. Seven p53+/+ mice exposed to 239PuO2 also developed pulmonary neoplasms, but the latency period for pulmonary neoplasia was significantly shorter in the p53+/ mice. Four pulmonary neoplasms were observed in p53+/- mice exposed to the higher dose of Be, whereas none were observed in the wild-type mice or in the heterozygous mice exposed to the lower dose of Be. Thus, both p53+/- and p53+/+ mice were susceptible to 239Pu-induced carcinogenesis, whereas the p53+/- but not the p53+/+ mice were susceptible to Be-induced carcinogenesis. However, only 2 pulmonary neoplasms (1 in each of the 239PuO2 exposure groups) were observed in the 59 p53+/ mice that were sacrificed or euthanatized within 9 mo after exposure, indicating that the p53+/- knockout mouse might not be appropriate for a 6-mo model of carcinogenesis for these inhaled carcinogens.

Responses of rat nasal epithelium to short- and long-term exposures of ozone: image analysis of epithelial injury, adaptation and repair

This article reviews the use of computerized image analysis and standard morphologic techniques to characterize the responses of nasal epithelium in laboratory rats to single or repeated exposures to a common urban air-pollutant, ozone. Alterations in the number and composition of the epithelial cell populations after either short- or long-term exposures are described. The principal nasal epithelial alteration induced by repeated exposures to this irritating, oxidant pollutant is mucous cell metaplasia (i.e., transformation of airway epithelium, normally devoid of mucous cells, to a secretory epithelium containing numerous mucus-secreting cells). This metaplastic change, induced by acute or chronic ozone exposures, has been morphometrically examined at various times post-exposure. In this article, we describe our current understanding of the pathogenesis and persistence of ozone-induced mucous cell metaplasia in nasal epithelium based on the results of these morphometric studies.

Failure of cigarette smoke to induce or promote lung cancer in the A/J mouse

A six-month bioassay in A/J mice was conducted to test the hypothesis that chronically inhaled mainstream cigarette smoke would either induce lung cancer or promote lung carcinogenicity induced by the tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Groups of 20 female A/J mice were exposed to filtered air (FA) or cigarette smoke (CS), injected with NNK, or exposed to both CS and NNK. At 7 weeks of age, mice were injected once with NNK; 3 days later, they were exposed to CS for 6 h/day, 5 days/week, for 26 weeks at a mean 248 mg total particulate matter/m3 concentration. Animals were sacrificed 5 weeks after exposures ended for gross and histological evaluation of lung lesions. No significant differences in survival between exposure groups was observed. A biologically significant level of CS exposure was achieved as indicated by CS-induced body weight reductions, lung weight increases, and carboxyhemoglobin levels in blood of about 17%. Crude tumor incidences, as determined from gross observation of lung nodules, were similar between the CS-exposed and FA groups, and the NNK and CS + NNK groups. Incidences in either of these latter groups were greater than either the CS or FA groups. Furthermore, tumor multiplicity in tumor-bearing animals was not significantly different among any of the three groups (FA, NNK, CS + NNK) in which tumors were observed. Thus, CS exposure neither induced lung tumors nor promoted NNK-induced tumors. Because the CS exposure concentration was probably near the maximally tolerable level, longer exposures should be evaluated to potentially establish a CS-induced model of lung carcinogenesis in the A/J mouse.

Particle clearance and histopathology in lungs of F344/N rats and B6C3F1 mice inhaling nickel oxide or nickel sulfate

The goals of this study were to (1) determine the effects of repeated inhalation of relatively insoluble nickel oxide (NiO) and highly soluble nickel sulfate hexahydrate (NiSO4.6H2O) on lung particle clearance, (2) investigate the effects of repeated inhalation of NiO or NiSO4 on the pulmonary clearance of subsequently inhaled 85Sr-labeled microspheres, (3) correlate the observed effects on clearance with accumulated Ni lung burden and associated pathological changes in the lung, and (4) compare responses in F344 rats and B6C3F1 mice. Male F344/N rats and B6C3F1 mice were exposed whole-body to either NiO or NiSO4.6H2O 6 hr/day, 5 days/week for up to 6 months. NiO exposure concentrations were 0, 0.62, and 2.5 mg NiO/m3 for rats and 0, 1.25, and 5.0 mg NiO/m3 for mice. NiSO4.6H2O exposure concentrations were 0, 0.12, and 0.5 mg NiSO4.6H2O/m3 for rats and 0, 0.25, and 1.0 mg NiSO4.6H2O/m3 for mice. After 2 and 6 months of whole-body exposure, groups of rats and mice were acutely exposed nose-only to 63NiO (NiO-exposed animals only), 63NiSO4.6H2O (NiSO4.6H2O-exposed animals only), or to 85Sr-labeled polystyrene latex (PSL) microspheres (both NiO- and NiSO4.6H2O-exposed animals) to evaluate lung clearance. In addition, groups of rats and mice were euthanized after 2 and 6 months of exposure and at 2 and 4 months after the whole-body exposures were completed to evaluate histopathological changes in the left lung and to quantitate Ni in the right lung. Repeated inhalation of NiO results in accumulation of Ni in lungs of both rats and mice, but to a greater extent in lungs of rats. During the 4 months after the end of the whole-body exposures, some clearance of the accumulated Ni burden occurred from the lungs of rats and mice exposed to the lower, but not the higher NiO exposure concentrations. Clearance of acutely inhaled 63NiO was also impaired in both rats and mice, with the extent of impairment related to both exposure concentration and duration. However, the clearance of acutely inhaled 85Sr PSL microspheres was not impaired. The repeated inhalation of NiO resulted in alveolar macrophage (AM) hyperplasia with accumulation of NiO particles in both rats and mice, chronic alveolitis in rats, and interstitial pneumonia in mice. These lesions persisted throughout the 4-month recovery period after the NiO whole-body exposures were terminated. In contrast, repeated inhalation of NiSO4.6H2O did not result in accumulation of Ni in lungs of either rats or mice and did not affect the clearance of 63NiSO4.6H2O inhaled after either 2 or 6 months of NiSO4.6H2O exposure. Clearance of the 85Sr-labeled microspheres was significantly impaired only in rats exposed to the microspheres after 2 months of exposure to NiSO4.6H2O. Histopathological changes in rats were qualitatively similar to those seen in NiO-exposed rats. Only minimal histopathological changes were observed in NiSO4.6H2O-exposed mice. These results suggest that repeated inhalation of NiO at levels resulting in AM hyperplasia and alveolitis may impair clearance of subsequently inhaled NiO. The potential effects of repeated inhalation of soluble NiSO4.6H2O on the clearance of subsequently inhaled poorly soluble particles are less clear.

Comparative carcinogenic effects of nickel subsulfide, nickel oxide, or nickel sulfate hexahydrate chronic exposures in the lung

The relative toxicity and carcinogenicity of nickel sulfate hexahydrate (NiSO4.6H2O), nickel subsulfide (Ni3S2), and nickel oxide (NiO) were studied in F344/N rats and B6C3F1 mice after inhalation exposure for 6 h/day, 5 days/week for 2 years. Nickel subsulfide (0.15 and 1 mg/m3) and nickel oxide (1.25 and 2.5 mg/m3) caused an exposure-related increased incidence of alveolar/bronchiolar neoplasms and adrenal medulla neoplasms in male and female rats. Nickel oxide caused an equivocal exposure-related increase in alveolar/bronchiolar neoplasms in female mice. No exposure-related neoplastic responses occurred in rats or mice exposed to nickel sulfate or in mice exposed to nickel subsulfide. These findings are consistent with results from other studies, which show that nickel subsulfide and nickel oxide reach the nucleus in greater amounts than the do water-soluble nickel compounds such as nickel sulfate. It has been proposed that the more water-insoluble particles are phagocytized, whereas the vacuoles containing nickel migrate to the nuclear membrane, where they release nickel ions that effect DNA damage. The findings from these experimental studies show that chronic exposure to nickel can cause lung neoplasms in rats, and that this response is related to exposure to specific types of nickel compounds.

Comparative pulmonary toxicities and carcinogenicities of chronically inhaled diesel exhaust and carbon black in F344 rats

Diesel exhaust (DE) is a known pulmonary carcinogen in rats, and the carcinogenic response is known to require the presence of soot. Many estimates of human lung cancer risk from inhaled DE have been developed from rat bioassay data or from the comparative mutagenic potencies of DE soot extract and known human chemical carcinogens. To explore the importance of the DE soot-associated organic compounds in the lung tumor response of rats, male and female F344 rats were exposed chroni cally to diluted whole DE or aerosolized carbon black (CB) 16 hr/day, 5 days/week at target particle concentrations of 2.5 mg/m³ (LDE, LCB) or 6.5 mg/m³ (HDE, HCB) or to filtered air. The CB served as a surrogate for the elemental carbon matrix of DE soot. Considering both the mass fraction of solvent-extractable matter and its mutagenicity in the Ames Salmonella assay, the mutagenicity in revertants per unit particle mass of the CB was three orders of magnitude less than that of the DE soot. Both DE soot and CB particles accumulated progressively in the lungs of exposed rats, but the rate of accumulation was higher for DE soot. In general, DE and CB caused similar, dose-related, nonneoplastic lesions. CB and DE caused significant, exposure concentration-related increases, of similar magnitudes, in the incidences and prevalences of the same types of malignant and benign lung neoplasms in female rats. The incidences of neoplasms were much lower in males than females, and the mci dences were slightly higher among DE- than CB-exposed males. Survival was shortened in the CB-exposed males, and the short ened survival may have suppressed the expression of carcinoge nicity as measured by crude incidence. Logistic regression mod eling did not demonstrate significant differences between the carcinogenic potencies of CB and DE in either gender. The re sults suggest that the organic fraction of DE may not play an important role in the carcinogenicity of DE in rats.

Comparative pulmonary toxicities and carcinogenicities of chronically inhaled diesel exhaust and carbon black in F344 rats

Diesel exhaust (DE) is a known pulmonary carcinogen in rats, and the carcinogenic response is known to require the presence of soot. Many estimates of human lung cancer risk from inhaled DE have been developed from rat bioassay data or from the comparative mutagenic potencies of DE soot extract and known human chemical carcinogens. To explore the importance of the DE soot-associated organic compounds in the lung tumor response of rats, male and female F344 rats were exposed chronically to diluted whole DE or aerosolized carbon black (CB) 16 hr/day, 5 days/week at target particle concentrations of 2.5 mg/m3 (LDE, LCB) or 6.5 mg/m3 (HDE, HCB) or to filtered air. The CB served as a surrogate for the elemental carbon matrix of DE soot. Considering both the mass fraction of solvent-extractable matter and its mutagenicity in the Ames Salmonella assay, the mutagenicity in revertants per unit particle mass of the CB was three orders of magnitude less than that of the DE soot. Both DE soot and CB particles accumulated progressively in the lungs of exposed rats, but the rate of accumulation was higher for DE soot. In general, DE and CB caused similar, dose-related, nonneoplastic lesions. CB and DE caused significant, exposure concentration-related increases, of similar magnitudes, in the incidences and prevalences of the same types of malignant and benign lung neoplasms in female rats. The incidences of neoplasms were much lower in males than females, and the incidences were slightly higher among DE- than CB-exposed males. Survival was shortened in the CB-exposed males, and the shortened survival may have suppressed the expression of carcinogenicity as measured by crude incidence. Logistic regression modeling did not demonstrate significant differences between the carcinogenic potencies of CB and DE in either gender. The results suggest that the organic fraction of DE may not play an important role in the carcinogenicity of DE in rats.

A comparison of the inflammatory response of the lung to inhaled versus instilled particles in F344 rats

The potential pulmonary toxicity of poorly soluble airborne dusts generated in industrial and environmental settings is often evaluated by inhalation studies in rodents. Studies using intratracheal instillation of particles have been suggested as a less expensive alternative. We conducted a study to compare the inflammatory response of the lung to instilled versus inhaled particles. In one study, female F344/N rats, 11-13 weeks of age, were exposed for 6 hr/day, 5 days/week for 4 weeks by inhalation to 0, 0.1, 1.0, or 10 mg/m3 of either alpha-quartz (toxic particle) or TiO2 (relatively low toxicity particle) and the lung burdens were determined at 1 week after the end of the exposure. The lungs were evaluated by analysis of bronchoalveolar lavage fluid (BALF) at 1, 8, and 24 weeks after the end of the exposure and by histopathology at 24 weeks. In a second study, rats were exposed by instillation to the lung burdens present in the preceding study at 1 week after the inhalation exposure, and the rats were evaluated in the same manner as in the inhalation study. In general, the degree of alveolitis, as evaluated by histopathology and BALF analysis, was similar by the two methods of exposure. With lung burdens up to 750 micrograms/g lung, the TiO2 elicited no changes in BALF parameters at any time by either method of exposure, nor was any histopathology observed. The BALF changes elicited by alpha-quartz were of approximately the same magnitude and followed the same time course by either exposure method with the lowest dose delivered to the lung by either method being a "no-effect" dose. At the highest dose, microgranulomas were observed in bronchial-associated lymphoid tissue (BALT) in both sets of rats. However, the highest inhalation exposure induced pleural granulomatous lesions that were not observed in the animals instilled with alpha-quartz. The results indicate that the relative potentials of the two materials to produce bronchoalveolitis and granulomatous lesions in BALT could be appropriately evaluated using either intratracheal or inhalation exposures.

Effect of chronic cigarette smoke exposure on lung clearance of tracer particles inhaled by rats

Cigarette smoking can influence the pulmonary disposition of other inhaled materials in humans and laboratory animals. This study was undertaken to investigate the influence of cigarette smoke exposures of rats on the pulmonary clearance of inhaled, relatively insoluble radioactive tracer particles. Following 13 weeks of whole-body exposure to air or mainstream cigarette smoke for 6 hr/day, 5 days/week at concentrations of 0, 100, or 250 mg total particulate matter (TPM)/m3, rats were acutely exposed pernasally to 85Sr-labeled fused aluminosilicate (85Sr-FAP) tracer particles, then air or smoke exposures were resumed. A separate group of rats was exposed to the 85Sr-FAP then serially euthanized through 6 months after exposure to confirm the relative insolubility of the tracer particles. We observed decreased tracer particle clearance from the lungs that was smoke concentration-dependent. By 180 days after exposure to the tracer aerosol, about 14, 20, and 40% of the initial activity of tracer was present in control, 100 mg TPM/m3, and 250 mg TPM/m3 groups, respectively. Body weight gains were less in smoke-exposed rats than in controls. Smoke exposure produced lung lesions which included increased numbers of pigmented alveolar macrophages distributed throughout the parenchyma and focal collections of enlarged alveolar macrophages with concomitant alveolar epithelial hyperplasia and neutrophilic alveolitis. The severity of the lesions increased with smoke exposure duration and concentration to include interstitial aggregates of pigmented macrophages and interstitial fibrosis. Our data confirm previous findings that exposure to cigarette smoke decreases the ability of the lungs to clear inhaled materials. We further demonstrate an exposure-concentration related magnitude of effect, suggesting that the cigarette smoke-exposed rat constitutes a useful model for studies of the effects of cigarette smoke on the disposition of inhaled particles.

Pulmonary toxicity of inhaled diesel exhaust and carbon black in chronically exposed rats. Part I: Neoplastic and nonneoplastic lung lesions

This study compared the pulmonary carcinogenicities and selected noncancer effects produced by chronic exposure of rats at high rates to diesel exhaust and carbon black. The comparison was intended to provide insight into the likely importance of the mutagenic organic compounds associated with the soot portion of diesel exhaust in inducing pulmonary carcinogenicity in diesel exhaust-exposed rats. The role of the organic fraction has become important in judging the usefulness of the substantial data base on carcinogenicity in rats for predicting lung cancer risk for humans, and for determining the most appropriate method of extrapolating results across species and exposure concentrations. Rats were exposed chronically to either diesel exhaust or carbon black, which served as a surrogate for diesel exhaust soot with much reduced mutagenic activity associated with its organic fraction. The sequestration of particles in the lung and the induction of pulmonary neoplasia and non-neoplastic changes in the lung were compared in detail. Samples also were provided to collaborators to examine adduct formation in lung DNA and hemoglobin. Approximately 140 female and 140 male F344/N rats were exposed for 16 hours per day, 5 days per week for up to 24 months, beginning at eight weeks of age, to diesel exhaust or carbon black at 2.5 mg or at 6.5 mg particles/m3 of air, or to clean air as controls. The diesel exhaust was generated by light-duty engines burning certification fuel and operating on an urban-duty cycle. The carbon black was selected because it had particle size and surface area characteristics similar to those of diesel exhaust soot, but markedly less mutagenic activity associated with its organic fraction when analyzed using procedures typically used in studies of diesel soot. Rats were killed after 3, 6, 12, 18, or 23 months of exposure to measure lung and lung-associated lymph node burdens of particles, lung weight, bronchoalveolar lavage indicators of inflammation, DNA adducts in whole lung and alveolar type II cells, and chromosome injury in circulating lymphocytes, and to perform histopathologic assessment. In addition, after 3 and 18 months of chronic exposure, one group of rats was acutely exposed to radiolabeled carbon black particles or to fluorescent microspheres. These exposures were conducted to examine the clearance of radiolabeled particles and the sequestration of the fluorescent microspheres in the lungs. These experiments provided information on clearance overload and particle dosimetry. The growth characteristics of lung neoplasms also were examined by transplanting neoplastic cells into athymic mice.(ABSTRACT TRUNCATED AT 400 WORDS)

Thirteen-week, repeated inhalation exposure of F344/N rats and B6C3F1 mice to ferrocene

Ferrocene (dicyclopentadienyl iron; CAS No. 102-54-5) is a relatively volatile compound used as a chemical intermediate, a catalyst, and an antiknock additive in gasoline. This organometallic chemical is of particular interest because of its structural similarities to other metallocenes, some of which are carcinogenic. F344/N rats and B6C3F1 mice were exposed to 0, 3.0, 10, and 30 mg ferrocene vapor/m3, 6 hr/day, 5 days/week, for 13 weeks. During these exposures, no rats or mice died, nor were any clinical signs of ferrocene-related toxicity observed. At the end of the exposures, male rats exposed to the lowest and highest level of ferrocene had decreased body weight gains compared to filtered-air-exposed control male rats, while body weight gains for all groups of both ferrocene- and filtered-air-exposed female rats were similar. Male mice exposed to ferrocene had no differences in body weight gains, compared to controls, but female mice had decreases in body weight gains at the 10 and 30 mg/m3 exposure levels. There were exposure concentration- and exposure-time-related increases in lung burdens of iron. The mean iron lung burden in rats exposed to 30 mg ferrocene vapor/m3 for 90 days was four times greater than the burden in control rats. No exposure-related changes in respiratory function, lung biochemistry, bronchoalveolar lavage cytology, total lung collagen, clinical chemistry, and hematology parameters were observed. This suggests that the accumulations of iron in lung did not cause an inflammatory response nor any functional impairment of the lung. There were no indications of developing pulmonary fibrosis nor of any hematologic toxicity. No exposure-related gross lesions were seen in any of the rats or mice at necropsy. Exposure-related histopathologic alterations, primarily pigment accumulations, were observed in the nose, larynx, trachea, lung, and liver of both species, and in the kidneys of mice. Lesions were most severe in the nasal olfactory epithelium where pigment accumulation, necrotizing inflammation, metaplasia, and epithelial regeneration occurred. Nasal lesions were observed in all ferrocene-exposed animals and differed only in severity, which was dependent on the exposure concentration. Histochemical stains of these target tissues showed the presence of iron ions. The results suggest that the mechanism of ferrocene toxicity may be the intracellular release of ferrous ion through ferrocene metabolism, followed by either iron-catalyzed lipid peroxidation of cellular membranes or the iron-catalyzed Fenton reaction to form hydroxyl radicals that directly react with other key cellular components, such as protein or DNA.

The effect of exposure pattern on the accumulation of particles and the response of the lung to inhaled particles

We hypothesized that a rapid rate of delivery of particles to the lung would overwhelm the normal clearance mechanisms of the lung and result in a higher lung burden of particles and a greater inflammatory response than a slower rate of particle delivery. F344/N rats were exposed over a 12-week period to the same weekly concentration times time product of carbon black (CB) particles, but at three different exposure rates: 3.5 mg/m3, 16 hr/day, 7 days/week; 13 mg/m3, 6 hr/day, 5 days/week; or 98 mg/m3, 4 hr/day, 1 day/week. The intermediate exposure rate was chosen to mimic an occupational work week and to give an 8-hr, time-weighted average exposure equal to the threshold limit value (TLV) for nuisance dusts of the American College of Governmental Industrial Hygienists (10 mg/m3). Pure CB has a lower TLV, 3.5 mg/m3, than nuisance dusts, but this is based on avoidance of excessive dirtiness in the workplace, not on the toxicity of CB. Lung burdens of CB were measured after 3, 6, 9, and 12 weeks of exposure and at 4, 8, 12, 16, and 24 weeks after the exposure ended. The inflammatory response was quantified by analysis of bronchoalveolar lavage fluid (BALF) after 6 and 12 weeks of exposure and at 1, 12, and 24 weeks after exposure. The histopathology of the lung was evaluated at the end of the exposure and at 24 weeks after the exposure. Acquired lung burdens were between 3 and 4 mg/lung at the end of the exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

IV sedation in pediatric dentistry: an alternative to general anesthesia

This prospective study was conducted to determine the sedative effects of IV ketamine and fentanyl on vital signs and behavior. Twenty-seven children, classified as ASA I, with a mean age of 34 months, were studied. The dosages of IV ketamine and fentanyl given were 0.5 mg/kg and 0.5 mcg/kg, respectively, approximately every 15-20 min. The pulse rate averaged 125 throughout the case. Blood pressure averaged 112/64. The respiration rate averaged 22 breaths per min. Mean behavior composite scores were 1.9 at the initial examination and 3.3 during treatment. One child vomited during treatment. Post-treatment complications were discomfort in 19% (5), nausea in 22% (6), and vomiting in 15% (4) of the patients. We concluded that IV sedation of precooperative healthy pediatric patients with ketamine, fentanyl, and nitrous oxide/oxygen appears to be a safe and effective sedation modality with minimal side effects when administered and monitored by a qualified anesthetist, offering the practitioner an alternative to general anesthesia.

Two-week, repeated inhalation exposure of F344/N rats and B6C3F1 mice to ferrocene

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 B6C3F1 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Lung retention and binding of [14C]-1-nitropyrene when inhaled by F344 rats as a pure aerosol or adsorbed to carbon black particles

1-Nitropyrene (NP), as found in the environment, is more typically associated with carbonaceous particles than found as an aerosol of the pure compound. To determine whether (and why) an association with particles resulted in prolonged lung retention of NP, rats were exposed to 14C-NP as a pure aerosol or adsorbed on carbon black particles. Total 14C retained in the lung was greater at all times from 0.5 h to 30 d after exposure to 14C-NP adsorbed to carbon black particles than after exposure to pure 14C-NP (p less than .05). The fraction of total 14C in lung bound to carbon black particles decreased steadily with time after exposure, indicating in vivo removal of NP from the particles. At 0.5 h after exposure, the fraction of the estimated deposited 14C that was covalently bound to lung macromolecules was twofold greater for NP adsorbed on carbon black than for pure NP. Covalently bound 14C in lungs increased with time after exposure to 14C-NP adsorbed to carbon black, reaching levels of approximately 1% of the deposited radioactivity at 7-30 d after exposure, whereas levels of covalently bound 14C declined with time after exposure to pure NP. Thus, at 30 d after exposure, the amount of 14C covalently bound to lung macromolecules was approximately 10-fold greater (p less than .05) in rats that inhaled 14C-NP adsorbed on carbon black particles than in rats that inhaled pure 14C-NP aerosols. These results suggest that association of NP with carbon black particles augments the interaction of reactive metabolites of NP with target macromolecules. This phenomenon is thought to be related to the slow release of NP from carbon black particles, and may augment the biological effects of inhaled NP when adsorbed on carbon black or similar particles in the environment.

Factors affecting possible carcinogenicity of inhaled nitropyrene aerosols

Nitroaromatics in general, and 1-nitropyrene in particular, are potent bacterial mutagens and animal carcinogens. Their importance as possible human carcinogens is difficult to assess because they are usually found in the environment as the products of combustion processes, and so they usually exist with many other compounds associated with airborne particles. The experiments reported here were carried out to determine if the inhalation of particle-associated 1-nitropyrene, or the concomitant exposure to an irritant gas, would alter the tissue distribution of 1-nitropyrene or its metabolites, compared to their distribution after inhalation of pure 1-nitropyrene. These experiments were intended to yield insights into the mechanisms involved in the potential carcinogenicity of particle-associated nitroaromatics as inhaled in the environment from automotive emissions and other sources. Groups of Fischer 344 rats inhaled pure 14C-1-nitropyrene aerosols, with and without coexposure to 5 parts per million sulfur dioxide, or 14C-1-nitropyrene adsorbed onto gallium oxide particles, with and without coexposure to sulfur dioxide, for four weeks. Lung retention of 14C-1-nitropyrene was not prolonged by its association with gallium oxide particles or by coexposure to sulfur dioxide. There was a marked inflammatory and fibrogenic response to the gallium oxide particles. Another set of experiments was carried out in which rats were exposed to 14C-1-nitropyrene either as pure aerosol or adsorbed onto carbon black particles. The amount of 14C in the lung that was bound to carbon black particles steadily decreased with time after exposure, compared to total lung 14C, indicating removal of 14C from the particles. Thirty minutes after exposure, the amount of 14C covalently bound to lung macromolecules, expressed as a percentage of calculated deposited radioactivity, was twofold greater for 1-nitropyrene adsorbed onto carbon black than for 1-nitropyrene alone. The amount of covalently bound 14C increased with time after exposure to 14C-1-nitropyrene adsorbed onto carbon black, reaching a level of approximately 1 percent of deposited radioactivity, 10-fold greater than that seen with pure 14C-1-nitropyrene seven to 30 days after exposure. The level of covalently bound 14C declined steadily after exposure to pure 14C-1-nitropyrene. Carbon black particles associated with adsorbed 1-nitropyrene offer the potential of studying DNA adduct formation in the lung, because DNA modification might be greater after inhalation of 1-nitropyrene adsorbed onto carbon black than after inhalation of pure 1-nitropyrene or 1-nitropyrene associated with metal oxides, such as gallium oxide.(ABSTRACT TRUNCATED AT 400 WORDS)

Evaluation of a real-time aerosol monitor (RAM-S) for inhalation studies

Measurement of the aerosol concentration in inhalation toxicology studies is generally done by gravimetric and/or chemical analysis of filter samples taken over a known period of time at a fixed sampling flow rate. The value obtained represents the time-averaged concentration in an exposure chamber. However, the filter method does not provide information as to the stability of aerosol concentration in "real-time" nor as to the time required for the aerosol concentration to reach the target value during the start-up of exposures. In order to accomplish evaluation of aerosol stability and chamber rise and fall times, a direct measurement device is required. An available real-time aerosol monitor (RAM-S, GCA Corp., Bedford, MA) is a photometer which collects scattered light from an aerosol cloud at a 70 +/- 25 degrees angle. The output signal is 0 to 10 volt with three ranges corresponding to maximum aerosol concentrations of 200, 20, and 2 mg/m3. The performance of the RAM-S was evaluated in inhalation studies involving nickel sulfate hexahydrate, nickel oxide, nickel subsulfide, and azodicarbonamide. Several RAM-S units were calibrated by obtaining both filter samples and voltage readings of a RAM-S simultaneously. Results indicated that the response of the RAM-S instruments was linear. However, the voltage output per given aerosol concentration was different for each compound used. Furthermore, there was interinstrument variability in the voltage response to aerosol concentration of a given compound. At concentrations higher than 100 mg/m3, modification of the flow system in the RAM-S was made to increase the sheath air around the optical system and also to dilute the aerosol concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies of the temporal and spatial distribution of aerosols in multi-tiered inhalation exposure chambers

Two multi-tiered whole body inhalation exposure chambers with nominal volumes of 1 m3 (H-1000) and 2 m3 (H-2000) were evaluated for their performance in terms of the temporal and spatial distribution of test aerosols within the chamber. Parameters investigated included chamber type, single-chamber-single-aerosol generator versus two-chamber-single-aerosol generator systems, chamber air supply and exhaust systems, particle size, and aerosol diluter type. Results indicated that: 1) particle size has an effect on chamber aerosol concentration distribution, with the larger particle resulting in a higher variation; 2) the single-chamber-single-generator system is more stable than the two-chamber-single-generator system; 3) the H-2000 chamber has a lower aerosol spatial variability than the H-1000 chamber; and 4) the aerosol distribution within the chamber could be improved with the use of a newly designed diluter.