Steven K. Seilkop

Radiotoxicity of Inhaled 239PuO2 in Dogs

Abstract Muggenburg, B. A., Guilmette, R. A., Hahn, F. F., Diel, J. H., Mauderly, J. L., Seilkop, S. K. and Boecker, B. B. Radiotoxicity of Inhaled 239PuO2 in Dogs. Radiat. Res. 170, 736–757 (2008). Beagle dogs inhaled graded exposure levels of insoluble plutonium dioxide (239PuO2) aerosols in one of three monodisperse particle sizes at the Lovelace Respiratory Research Institute (LRRI) to study the life-span health effects of different degrees of α-particle dose non-uniformity in the lung. The primary noncarcinogenic effects seen were lymphopenia, atrophy and fibrosis of the thoracic lymph nodes, and radiation pneumonitis and pulmonary fibrosis. Radiation pneumonitis/ pulmonary fibrosis occurred from 105 days to more than 11 years after exposure, with the lowest associated α-particle dose being 5.9 Gy. The primary carcinogenic effects also occurred almost exclusively in the lung because of the short range of the α-particle emissions. The earliest lung cancer was observed at 1086 days after the inhalation exposure. The most common type seen was papillary adenocarcinoma followed by bronchioloalveolar carcinoma. These lung cancer results indicate that a more uniform distribution of α-particle dose within the lung has an equal or possibly greater risk of neoplasia than less uniform distributions of α-particle dose. The results are consistent with a linear relationship between dose and response, but these data do not directly address the response expected at low dose levels. No primary tumors were found in the tracheobronchial and mediastinal lymph nodes despite the high α-particle radiation doses to these lymph nodes, and no cases of leukemia were observed.

Health effects of subchronic inhalation exposure to simulated downwind coal combustion emissions

Context: There have been no animal studies of the health effects of repeated inhalation of mixtures representing downwind pollution from coal combustion. Environmental exposures typically follow atmospheric processing and mixing with pollutants from other sources. Objective: This was the fourth study by the National Environmental Respiratory Center to create a database for responses of animal models to combustion-derived pollutant mixtures, to identify causal pollutants—regardless of source. Methods: F344 and SHR rats and A/J, C57BL/6, and BALB/c mice were exposed 6 h/day 7 days/week for 1 week to 6 months to three concentrations of a mixture simulating key components of “downwind” coal combustion emissions, to the highest concentration filtered to remove particulate matter (PM), or to clean air. Emissions from low-sulfur subbituminous coal were modified to create a mixture recommended by an expert workshop. Sulfur dioxide, nitrogen oxides, and PM were the dominant components. Nonanimal-derived PM mass concentrations of nominally 0, 100, 300, and 1000 µg/m3 were mostly partially neutralized sulfate. Results: Only17 of 270 species-gender-time-outcome comparisons were significantly affected by exposure; some models showed no effects. There was strong evidence that PM participated meaningfully in only three responses. Conclusion: On a total mass or PM mass basis, this mixture was less toxic overall than diesel and gasoline exhausts or wood smoke. The largely sulfate PM contributed to few effects and was the sole cause of none. The study did not allow identification of causal pollutants, but the potential role of NOx in some effects is suggested by the literature.

Effects of simulated downwind coal combustion emissions on pre-existing allergic airway responses in mice

Context: Coal-fired power plant emissions can contribute a significant portion of the ambient air pollution in many parts of the world. Objective: We hypothesized that exposure to simulated downwind coal combustion emissions (SDCCE) may exacerbate pre-existing allergic airway responses. Methods: Mice were sensitized and challenged with ovalbumin (OVA). Parallel groups were sham-sensitized with saline. Mice were exposed 6 h/day for 3 days to air (control, C) or SDCCE containing particulate matter (PM) at low (L; 100 μg/m3), medium (M; 300 μg/m3), or high (H; 1000 μg/m3) concentrations, or to the H level with PM removed by filtration (high-filtered, HF). Immediately after SDCCE exposure, mice received another OVA challenge (pre-OVA protocol). In a second (post-OVA) protocol, mice were similarly sensitized but only challenged to OVA before air/SDCCE. Measurement of airway hyperresponsiveness (AHR), bronchoalveolar lavage (BAL), and blood collection were performed ~24 h after the last exposure. Results: SDCCE significantly increased BAL macrophages and eosinophils in OVA-sensitized mice from the post-OVA protocol. However, there was no effect of SDCCE on BAL macrophages or eosinophils in OVA-sensitized mice from the pre-OVA protocol. BAL neutrophils were elevated following SDCCE in both protocols in nonsensitized mice. These changes were not altered by filtering out the PM. In the post-OVA protocol, SDCCE decreased OVA-specific IgG1 in OVA-sensitized mice but increased levels of total IgE, OVA-specific IgE and OVA-specific IgG1 and IgG2a in non-sensitized animals. In the pre-OVA protocol, SDCCE increased OVA-specific IgE in both sensitized and non-sensitized animals. Additionally, BAL IL-4, IL-13, and IFN-γ levels were elevated in sensitized mice. Conclusion: These results suggest that acute exposure to either the particulate or gaseous phase of SDCCE can exacerbate various features of allergic airway responses depending on the timing of exposure in relation to allergen challenge.

Mutational analysis of the mitochondrial tRNA genes and flanking regions in umbilical cord tissue from uninfected infants receiving AZT-based therapies for prophylaxis of HIV-1

A sensitive vertical denaturing gradient gel electrophoresis (DGGE) method, using 13 unipolar psoralen‐clamped PCR primer pairs, was developed for detecting sequence variants in the 22 tRNA genes and flanking regions (together spanning ∼21%) of the human mitochondrial genome. A study was conducted to determine (i) if mitochondrial DNA (mtDNA) polymorphisms and/or mutations were detectable in healthy newborns and (ii) if prepartum 3′‐azido‐2′,3′‐dideoxythymidine (AZT) based HIV‐1 prophylaxis was associated with significant increases in mtDNA mutations and changes in the degree of heteroplasmy of sequence variants in uninfected infants born to HIV‐1‐infected mothers. DGGE analysis of umbilical cord tissue (where vascular endothelium and smooth muscle cells are the major source of mtDNA) showed that mtDNA sequence variants were significantly elevated by threefold in AZT‐treated infants compared with unexposed controls (P < 0.001), with 24 changes observed in 19/52 (37%) treated newborns (averaging 0.46 changes/subject) versus only eight changes found in 7/55 (13%) unexposed newborns (averaging 0.15 changes/subject). Six distinct sequence variants occurring in unexposed controls were predominately synonymous and homoplasmic, representing previously reported polymorphisms. Uninfected infants exposed to a combination of AZT and 2′,3′‐dideoxy‐3′‐thiacytidine and “maternal HIV‐1” had a significant shift in the spectrum of mutations (P = 0.04) driven by increases in nonsynonymous heteroplasmic sequence variants at polymorphic sites (10 distinct variants) and novel sites (four distinct variants). While the weight of evidence suggests that prepartum AZT‐based prophylaxis produces mtDNA mutations, additional research is needed to determine the degree to which fetal responses to maternal HIV‐1 infection, in the absence of antiretroviral treatment, contribute to prenatal mtDNA mutagenesis. Environ. Mol. Mutagen., 2009.

The evaluation of long-term sulfur deposition models

Abstract The International Sulfur Deposition Model Evaluation (ISDME) assessed the performance of 11 regional, long-term deposition models in predicting amounts of sulfur wet deposition. With few exceptions, each model predicted air concentrations and dry/wet deposition amounts of SO2 and SO42− at up to 66 sites across eastern North America for each season of 1980. Unlike its predecessors, this evaluation focused on the ability of the models to replicate, within the uncertainty limits of the data, the magnitude and position of the seasonal spatial patterns of S wet deposition. Both the spatial patterns and the uncertainties arising from measurement and interpolation errors were determined by a simple Kriging technique. Model performance measures included the per cent of subrogions where interpolated predictions and observations were significantly different and differences between the magnitudes and locations of maxima, centroids and orientations of the major axes. When data uncertainty limits are considered, the seasonal predictions of one Lagrangian and two statistical models were insignificantly different from the seasonal observations (at approximately the 95% confidence level) across at least 85% of the evaluation region. Three other models performed relatively well for two or three seasons, while the performance of three others was somewhat erratic. The final two models significantly underpredicted for every season across at least 40% of the evaluation region. In spring, all of the models correctly predicted the location of the observed maximum amount of S wet deposition. For the other three seasons the models predicted the locations within 170–350 km. Except for summer, most models predicted the magnitude of the observed maximum within the data uncertainty limits.

Radiotoxicity of inhaled (239)PuO(2) in dogs.

Abstract Muggenburg, B. A., Guilmette, R. A., Hahn, F. F., Diel, J. H., Mauderly, J. L., Seilkop, S. K. and Boecker, B. B. Radiotoxicity of Inhaled 239PuO2 in Dogs. Radiat. Res. 170, 736–757 (2008). Beagle dogs inhaled graded exposure levels of insoluble plutonium dioxide (239PuO2) aerosols in one of three monodisperse particle sizes at the Lovelace Respiratory Research Institute (LRRI) to study the life-span health effects of different degrees of α-particle dose non-uniformity in the lung. The primary noncarcinogenic effects seen were lymphopenia, atrophy and fibrosis of the thoracic lymph nodes, and radiation pneumonitis and pulmonary fibrosis. Radiation pneumonitis/ pulmonary fibrosis occurred from 105 days to more than 11 years after exposure, with the lowest associated α-particle dose being 5.9 Gy. The primary carcinogenic effects also occurred almost exclusively in the lung because of the short range of the α-particle emissions. The earliest lung cancer was observed at 1086 days after the inhalation exposure. The most common type seen was papillary adenocarcinoma followed by bronchioloalveolar carcinoma. These lung cancer results indicate that a more uniform distribution of α-particle dose within the lung has an equal or possibly greater risk of neoplasia than less uniform distributions of α-particle dose. The results are consistent with a linear relationship between dose and response, but these data do not directly address the response expected at low dose levels. No primary tumors were found in the tracheobronchial and mediastinal lymph nodes despite the high α-particle radiation doses to these lymph nodes, and no cases of leukemia were observed.

The National Environmental Respiratory Center (NERC) experiment in multi-pollutant air quality health research: III. Components of diesel and gasoline engine exhausts, hardwood smoke and simulated downwind coal emissions driving non-cancer biological responses in rodents.

Abstract An approach to identify causal components of complex air pollution mixtures was explored. Rats and mice were exposed by inhalation 6 h daily for 1 week or 6 months to dilutions of simulated downwind coal emissions, diesel and gasoline exhausts and wood smoke. Organ weights, hematology, serum chemistry, bronchoalveolar lavage, central vascular and respiratory allergic responses were measured. Multiple additive regression tree (MART) analysis of the combined database ranked 45 exposure (predictor) variables for importance to models best fitting 47 significant responses. Single-predictor concentration-response data were examined for evidence of single response functions across all exposure groups. Replication of the responses by the combined influences of the two most important predictors was tested. Statistical power was limited by inclusion of only four mixtures, albeit in multiple concentrations each and with particles removed for some groups. Results gave suggestive or strong evidence of causation of 19 of the 47 responses. The top two predictors of the 19 responses included only 12 organic and 6 inorganic species or classes. An increase in red blood cell count of rats by ammonia and pro-atherosclerotic vascular responses of mice by inorganic gases yielded the strongest evidence for causation and the best opportunity for confirmation. The former was a novel finding; the latter was consistent with other results. The results demonstrated the plausibility of identifying putative causal components of highly complex mixtures, given a database in which the ratios of the components are varied sufficiently and exposures and response measurements are conducted using a consistent protocol.

Carcinogenic interactions between a single inhalation of 239PuO2 and chronic exposure to cigarette smoke in rats.

Abstract Rats were exposed once by inhalation to plutonium-239 dioxide (239PuO2), resulting in chronic α-particle irradiation of the lung, and exposed chronically to cigarette smoke to examine carcinogenic interactions between the two exposures. F344 rats were exposed to 239PuO2 to achieve an initial lung burden of 0.5 kBq and then exposed 6 h/day, 5 days/week to cigarette smoke at 100 or 250 mg particulate matter/m3 for up to 30 months. Exposure to cigarette smoke increased the cumulative radiation dose to lung by slowing the clearance of 239PuO2. 239PuO2 alone did not affect survival, but the higher cigarette smoke exposure shortened survival in females. Combined exposure to 239PuO2 and cigarette smoke acted synergistically to shorten survival in both genders. The combined effects of cigarette smoke and 239PuO2 were approximately additive for lung hyperplasia and adenomas but were strongly synergistic for carcinomas. Differences between observed incidences and incidences predicted by survival-adjusted models accounting for increased radiation dose revealed a substantial component of synergy for carcinomas above that attributable to the radiation dose effect. The synergy for malignant lung tumors is consistent with findings from uranium miners and nuclear weapons production workers. These results bolster confidence in the epidemiological findings and have implications for risk assessment.

Biokinetics of systemically distributed 60Co in the rat: an experimental model useful in evaluating medical countermeasures for internal contamination.

Abstract LBERI, a member of the Medical Countermeasures to Radiologic Threats (MCART) consortium funded by NIAID, was tasked to develop biokinetic models for the distribution of radionuclide threats using the most likely routes of incorporation in both small and large animals. In this paper, the biokinetics of systemically administered soluble 60Co have been examined. Male and female jugular-vein-catheterized (JVC) F344 rats received intravenous (IV) doses of 11.2 kBq of 60CoCl2. The distribution of the radiocobalt was followed for 28 d with tissue sampling done at 1 and 4 h, and at 1, 2, 4, 8, 16, and 28 d. Urine and feces were collected daily. Tissues and excreta were analyzed by gamma pulse height analysis. Within 8 d, 93% of the cobalt was eliminated from the body, primarily though urine. The highest tissue burdens were found in the liver, gastrointestinal (GI) tract, and muscle shortly after administration. These tissues cleared quickly, so that by the conclusion of the 28-d study, less than 3% of the injected dose remained in the body. The results are comparable to published literature values for tissue content of 60Co and for excretion patterns up to 30 d after injection. These results will provide the data needed to construct a biokinetic model for the unperturbed biokinetics of 60Co in rats, which will subsequently be used to evaluate the impact of administered decorporating agents on organ radiation doses. The animal model described in this paper is representative of that used for other routes of radionuclide administration, such as inhalation, ingestion, and wound contamination, that have been studied at LBERI in support of the MCART and NIAID programs.

Radiotoxicity of Inhaled239PuO2in Dogs

Abstract Muggenburg, B. A., Guilmette, R. A., Hahn, F. F., Diel, J. H., Mauderly, J. L., Seilkop, S. K. and Boecker, B. B. Radiotoxicity of Inhaled 239PuO2 in Dogs. Radiat. Res. 170, 736–757 (2008). Beagle dogs inhaled graded exposure levels of insoluble plutonium dioxide (239PuO2) aerosols in one of three monodisperse particle sizes at the Lovelace Respiratory Research Institute (LRRI) to study the life-span health effects of different degrees of α-particle dose non-uniformity in the lung. The primary noncarcinogenic effects seen were lymphopenia, atrophy and fibrosis of the thoracic lymph nodes, and radiation pneumonitis and pulmonary fibrosis. Radiation pneumonitis/ pulmonary fibrosis occurred from 105 days to more than 11 years after exposure, with the lowest associated α-particle dose being 5.9 Gy. The primary carcinogenic effects also occurred almost exclusively in the lung because of the short range of the α-particle emissions. The earliest lung cancer was observed at 1086 days after the inhalation exposure. The most common type seen was papillary adenocarcinoma followed by bronchioloalveolar carcinoma. These lung cancer results indicate that a more uniform distribution of α-particle dose within the lung has an equal or possibly greater risk of neoplasia than less uniform distributions of α-particle dose. The results are consistent with a linear relationship between dose and response, but these data do not directly address the response expected at low dose levels. No primary tumors were found in the tracheobronchial and mediastinal lymph nodes despite the high α-particle radiation doses to these lymph nodes, and no cases of leukemia were observed.