Edward B. Barr

Comparative Pulmonary Toxicities and Carcinogenicities of Chronically Inhaled Diesel Exhaust and Carbon Black in F344 Rats

Abstract 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.

EFFECTS OF CIGARETTE SMOKE EXPOSURE AND CESSATION ON INFLAMMATORY CELLS AND MATRIX METALLOPROTEINASE ACTIVITY IN MICE

B6C3F1 female mice were exposed to cigarette smoke (CS) (250 mg/m3 total particulate material) or filtered air (FA), 6 hours/day, 5 days/week, for 6, 7, or 10 weeks, or to CS for 6 weeks, then FA for 1 or 4 additional weeks. Exposure to CS increased macrophages, neutrophils, lymphocytes, and matrix metalloproteinase (MMP)-2 and MMP-9 content in bronchoalveolar lavage fluid. Partial recovery of most lavage parameters (except lymphocytes) was observed 1 week after cessation of CS exposure with further reductions after 4 weeks, but interstitial inflammation persisted longer. These results support a role for MMPs in CS-induced emphysema and indicate that smoking cessation allows restoration toward normal homeostasis.

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.

Design, characterization, and evaluation of a small-scale diesel exhaust exposure system

A single-cylinder engine diesel exhaust exposure system was constructed to conduct laboratory health effects studies. The single-cylinder engine was selected to provide a cost-effective and easy-to-operate biological exposure system as an alternative to larger engines operated on chassis or test stand dynamometers. The engine was a 5500-watt diesel generator operated at load by connection to a bank of 11 500 watt light sources. The engine was isolated from the rodent and cell exposure chambers to ameliorate excessive noise and heat in the exposure room. Exhaust was diluted approximately 100:1 and routed to a 1 m3 flow-through exposure chamber where the exhaust composition was assessed in detail. Measurements included particle mass, particle size distribution (based on both number and mass), carbon monoxide, nitrogen oxides, particle carbon (organic and elemental), particle sulfate/nitrate, metals, total and speciated volatile hydrocarbons, and speciated semivolatile and particle-phase polycyclic aromatic hydrocarbons. The exhaust composition was compared with published diesel exhaust compositions and that from a 2000 Model Cummins 5.9L ISB engine, which was operated on a variable duty cycle on a dynamometer using the same fuel and lube oil as the single-cylinder engine. The exhaust composition from the single-cylinder engine was consistent with “typical” diesel exhaust and the larger on-road engine. It yielded particle mass with a mass median diameter of ∼0.1 𝛍m that was composed of ∼70% elemental carbon, ∼35% organic carbon, ∼4–5% sulfate/nitrate, and small amounts of metals. The volatile and speciated organic/inorganic gases were in the range of literature values, with specific characteristics of low particle bound aromatic compounds and higher amounts of volatile and oxygenated organics. Based on this evaluation, the single-cylinder engine and exhaust dilution system described here generates emissions that should be useful for studying health hazards that pertain to emissions from a broad range of diesel engines.

Fate of Inhaled Nickel Oxide and Nickel Subsulfide in F344/N Rats

AbstractThe fates of inhaled nickel oxide (NiO, green oxide calcined at 1200°C) and nickel subsulfide (Ni3S2), two occupationally relevant nickel compounds, have been studied in male F344/N rats. Groups of rats underwent pernasal exposure to 9.9 mg NiO/m3 or to 5.7 mg Ni3S2/m3 for 70 and 120 min, respectively. The activity median aerodynamic diameters (geometric standard deviation) of the NiO and Ni3S2 aerosols were 1.3 μm (2.0) and 1.3 μm (1.5), respectively. End points evaluated included total and regional respiratory tract deposition of the aerosols, lung clearance of deposited material, distribution of solubilized material to extrarespiratory tract tissue, and pathways of Ni excretion from the body. The fractions of the inhaled NiO and Ni3S2 aerosols that deposited in the respiratory tract were 0.11 and 0.13, respectively. The fractions of the inhaled aerosol that deposited in the lungs were 0.05 for both aerosols. Inhaled NiO cleared slowly from the lungs, with a half-life of approximately 120 days. ...

INFLUENCE OF ADSORPTION TO CARBON BLACK PARTICLES ON THE RETENTION AND METABOLIC ACTIVATION OF BENZO(a)PYRENE IN RAT LUNGS FOLLOWING INHALATION EXPOSURE OR INTRATRACHEAL INSTILLATION

AbstractThere is a need to define the influence of adsorption of organic compounds onto particles on the biological fate of these compounds when inhaled. In this study, rats were exposed by nose-only inhalation (2 h) to 2 mg/m3 or 20 mg/m3 of pure [14C]BaP or [14C]BaP adsorbed onto carbon black particles at 0.2 mg/m3, 2.0 mg/m3, or 20 mg/m3 (total mass concentration ≃ 100 mg/m3). In separate studies, rats were intratracheally instilled with amounts of pure [14C]BaP and [14C]BaP on carbon black that were similar to those deposited in lungs by inhalation. In all cases, clearance of 14C from lungs had a rapid short-term component and a slower long-term component of clearance. As a percentage of the calculated initial lung deposition after inhalation or instillation, the long-term retention of 14C was similar for all amounts of pure [14C]BaP used and also similar for both methods of administration. The long-term lung retention of 14C as a percentage of the initial lung deposition was increased 16–60 times as ...

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.

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.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.

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 μg). Additional wild-type p53 +/- mice were exposed by inhalation to either 500 Bq of 239PuO2 or 60 μg 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 53 +/- 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.