2001 Progress Report: Animal Models: Dosimetry, and Pulmonary and Cardiovascular Events

EPA Grant Number: R827354C004
Subproject: this is subproject number 004 , established and managed by the Center Director under grant R827354
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: Airborne PM - Rochester PM Center
Center Director: Oberdörster, Günter
Title: Animal Models: Dosimetry, and Pulmonary and Cardiovascular Events
Investigators:
Current Investigators: Oberdörster, Günter , Elder, Alison C.P.
Institution:
Current Institution: University of Rochester
EPA Project Officer:
Project Period: June 1, 1999 through May 31, 2005 (Extended to May 31, 2006)
Project Period Covered by this Report: June 1, 2001 through May 31, 2002
RFA: Airborne Particulate Matter (PM) Centers (1999) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Particulate Matter , Air

Objective:

Earlier studies have shown that ultrafine particles elicit significantly greater pulmonary inflammatory responses than larger particles of the size of the accumulation mode when administered at the same mass to the respiratory tract. The hypothesis for this research is that ultrafine particles in the urban atmosphere contribute to the adverse health effects associated with particulate matter (PM). The objectives of the animal studies are to evaluate pulmonary and cardiovascular effects of inhaled laboratory-generated ultrafine and fine carbon particles using animal models of increased susceptibility and to obtain data on the deposition and subsequent fate of inhaled ultrafine particles.

Progress Summary:

Based on extensive critical discussions among the scientists of all five Research Cores and input from our Science Advisory Committee (SAC) members, a major effort in this Core was devoted to improving the generation system for laboratory-generated ultrafine carbon particles with respect to eliminating organic contaminants and setting up a separate system for generation of ultrafine organic particles and of mixed ultrafine carbon/iron particles. We continued work on our general hypothesis, that pre-existing inflammation and old age are important priming factors to sensitize the host for subsequent pulmonary and cardiovascular effects of inhaled ultrafine particles. The in vivo endpoints include pulmonary inflammatory markers, analysis of blood white cell adhesion molecules, blood coagulation factors, heart rate variability, and blood pressure (BP) variability. A general study design for rats and mice includes an inflammatory priming event (inhaled low dose endotoxin lipopolysaccharide (LPS) or intratracheal human influenza virus) followed by ultrafine particles inhalation exposure (ultrafine carbon with or without mixed in iron) and with or without ozone (as a frequently occurring co-pollutant). The priming of the respiratory tract is done to mimic the elderly group with respiratory tract inflammation identified in particulate matter (PM) epidemiological studies as showing increased morbidity/mortality associated with PM exposure. We selected endotoxin as a priming agent because gram-negative bacteria, the source of endotoxin, have been found in several studies as the cause for pneumonia and bronchitis in people with chronic obstructive pulmonary disease (COPD).

The design of these animal studies comprised of 16 different groups, including a sham-exposed control group. Young (8-10 weeks old) and old (20-22 months old) rats and mice were exposed for 6 hours after priming to the ultrafine particles, with or without ozone, and sacrificed 24 hours later. Endpoints included analysis of cellular (including chemiluminescence) and biochemical lung lavage parameters, blood cell and plasma cytokine, and acute phase proteins. Results were analyzed by a four-way ANOVA, with UFPs, ozone, age, and the priming agent being the four factors. This study design based on the results from 16 experimental groups represents a powerful tool to evaluate main effects and interactions. By examining the three treatments in combination with each other and with age, possible interactive or synergistic effects can be understood. Such interactive effects will provide a basis for designing subsequent mechanistic studies.

We also extracted ribonucleic acid (RNA) from lungs, hearts, and livers for analysis of gene expression using micro-array technology to identify changes in oxidative stress-related genes and others as a basis for subsequent mechanistic studies.

A continued focus of this research was the development, characterization, and use of compromised animal models which included improving the analysis of rat electrocardiogram (ECG) recordings from radio-transmitter implants. Furthermore, we continued our dosimetry studies using carbon-13 (13C) ultrafine particles to determine deposition in the lung and translocation to extrapulmonary tissues. We also have performed preliminary experiments using ultrafine fluorescent beads to evaluate ultrafine particle translocation from the conducting airways to the ganglia in the neck along sensory nerves. Finally, we have initiated a collaborative study with the Harvard PM Center using their ultrafine ambient particle concentrator to expose normal old rats and spontaneously hypertensive (SHR) old rats implanted with radio-transmitters for recording of ECG, BP, and body temperature. A summary of these studies is provided below.

Studies with Mixed Inorganic and with Organic Ultrafine Particles

We have performed 6-hour exposures of groups of young (8 weeks) and aged (18 months) mice to the mixed carbon/iron (C/Fe) ultrafine particles at approximately 100 micrograms (µg)/m3, with and without prior priming by inhaled low dose LPS, and with and without additional exposure to ozone (0.5 ppm). Similar to our earlier studies in rats (Elder, et al. 2000b), age and UFPs showed a significant effect in that lavaged inflammatory cells of old mice with a greater release of reactive oxygen species in an ex vivo assay performed 24 hours post-exposure. We also have first results of the toxicogenomic RNA analysis of lungs and heart which again show striking differences between responses of old and young mice. Young animals exposed to the combination of ultrafine particles and ozone after priming with inhaled LPS, showed a significant increase not only in inflammatory cytokines and chemokines, but also in anti-inflammatory genes (IL-6, IL-10). This was not found in the old mice. This implies that the old organism may not be able to mount an efficient anti-inflammatory response, which reflects a contrast to the response of the young organism. The RNA from the heart also showed differences between young and old mice (see Figure 1); the expression of antioxidant proteins 1 and 2 (AOP1, AOP2) were significantly increased in old animals but not in young animals at 24 hours post-exposure. In addition, at least two-fold expression of many more oxidative stress-related genes was found in the hearts of old mice than in the hearts of young mice after exposure, indicating that the old organism is much more susceptible to cardiac effects than the young organism following inhalation of air pollutants.

Figure 1. Micro-array Results of Cardiac Gene Expression in Old and Young LPS-primed Mice Following Inhalation Exposure to Ultrafine Mixed Carbon/Iron Particles in Combination with Ozone

The results of the micro-array analysis were confirmed by Northern slot blot analysis. Once all the results of this study are available, we will subject them to a 4-way ANOVA to determine the main effects and interactions of ultrafine particles, age, ozone, and LPS priming. We plan to perform additional studies with inclusion of sacrifice times prior to and beyond 24 hours. Results of these studies will be an important feedback for both our ongoing controlled clinical and epidemiological studies, with regard to inclusion of potential additional endpoints in those studies.

A second study was performed with the same study design of 6-hour exposures of old and young mice to ultrafine C/Fe particles with and without ozone and with and without priming using intratracheal influenza virus. The results of the 4-way ANOVA showed that: (1) the ultrafine C/Fe particles had a main effect for the endpoints lavaged polymorphonuclear leukocytes (PMNs) and reactive oxygen species (ROS) release of lavage cells; (2) age had a main effect; (3) additional significant interactions with the ultrafine particles were present leading to greater responses in the aged organism; and (4) ozone and virus priming also had significant main effects and interactions with the ultrafine particles. Some of the endpoints are still being analyzed and results are forthcoming. These are intercellular adhesion molecule-1 (ICAM-1) expression on PMNs, monocytes, and lymphocytes of the blood and of lavage cells; acute phase proteins and coagulation factors in plasma, which will allow us to compare responses seen in the animal studies with the clinical and epidemiological studies.

Other studies with laboratory-generated ultrafine carbon particles were performed in old rats with and without prior endotoxin priming via intraperitioneal (i.p.) injection, to simulate the early phase of a systemic inflammatory stimulus. Twenty-month old normal Fischer rats and 15-month old spontaneously hypertensive rats (SHR) were used for a 6 hour ultrafine particle exposure, with or without the i.p. LPS priming treatment. Inflammatory lung lavage and blood parameters were determined, including measurement of intracellular ROS generation by inflammatory pulmonary and blood cells. Results confirmed a significant main effect for the ultrafine particles, as well as the priming treatment. Results of several other endpoints are not yet available and will be updated with the next report.

Table 1 summarizes the main effects of ultrafine particles for some endpoints of our rodent studies after respiratory tract or i.p. priming. Significant respiratory and systemic effects have been found, which together with results from controlled clinical studies confirm that laboratory-generated ultrafine carbon particles and C/Fe particles can, indeed, cause acute responses.

Table 1. Summary of Main Effects (Positive) of Inhaled Ultrafine Carbon or Carbon/Iron Particles (UFP); Priming In Rodents For Some Pulmonary and Vascular Endpoints; Ozone; and Age

Investigators from across the Center collaborated to characterize our spark discharge generated ultrafine carbon particles as described in last year's progress report. Further analysis of these particles using extraction and gas chromotography mass spectrometry (GCMS) analysis showed fragments characteristic of long chain saturated hydrocarbons/acids/alcohols, which amounted to slightly less than 4 percent of the total mass.

A new research initiative was initiated to investigate effects of organic ultrafine particles, which are a major fraction of urban ultrafines, as determined by the Center's ultrafine particle characterization studies (see report for R827354C001). We developed methodologies for generating an ultrafine condensation aerosol from C20 and C30 compounds and from new and used motor oil. Methods included use of an electrospray nozzle, heating in a tube furnace and subsequent cooling with and without seed nuclei. These early efforts to generate organic ultrafine particles have been continued by Dr. John Veranth, University of Utah, as a Center Visiting Scientist (see report for R827354C0008).

Development and Characterization of Compromised Animal Model

Analysis of HRV and repolarization segment in unrestrained rats using a telemetry system. Parallel to the evaluation of the ECG recordings from the epidemiological and clinical PM Center studies, scientists in our cardiac core have developed an algorithm for analysis of recorded ECG and BP signals of rats. In our preliminary analysis of heart rate variability (HRV) in rats, we developed a program to analyze ECG recordings obtained using a telemetry system with implantable transmitters. The analysis of variability of the HRV parameters led us to conclude that at least 1,500 beats are needed to obtain reliable and reproducible estimation of HRV parameters (Couderc, et al., 2002). Thus, in our current experiment, we increased the length of the ECG recordings to insure better estimation of HRV parameters.

Our program has been modified to analyze both ECG and BP signals. The BP signal is often easier to analyze and often of better quality (with less electromyogram) than the ECG. From BP, similar HRV estimators can be computed. Currently, our program analyzes long-term recordings of ECG and BP signals (24-hours) with the possibility of scanning the entire period to locate stable and noise-free signal sequences.

In addition, we currently are working on a new tool for the analysis of the repolarization interval from the ECG signals of rats. Recent experimental findings reported in the literature show that modifications of ionic channel functions by pharmacological agents, ischemia, or electrolyte abnormalities generate repolarization abnormalities with increased heterogeneity of repolarization. These repolarization abnormalities are associated with increased risk of ventricular arrhythmias leading to episodes of torsades de pointes with subsequent ventricular fibrillation. These experimental data confirm long-term clinical experience indicating the association between prolonged (and abnormal) repolarization and sudden cardiac death. Exposure to particulate air pollution has been shown to be associated with an increased risk of cardiac death in animals, where predominantly elderly patients with existing cardio pulmonary disease appear to be at risk. Researchers have found that air pollution may affect the myocardium at the cellular level by modifying intrinsic electrical properties of the myocardial cell through direct (blood-born or reflex-based) or indirect (inflammatory) mechanisms.

Our program will measure QT and QT peak interval duration by identifying the beginning of the QRS complex and the peak and end of the T-wave. Normal QT and QT peak values will be determined based on a series of baseline recordings in normal rats and using heart rate adjustment formula. The T-wave area analysis will be used to quantify repolarization morphology by tracking the distribution of the amplitude along the time axis. The measure of T-wave morphology has the benefits of being less noise dependent and also is less dependent on accurate detection of the end of the T-wave.

Our work focuses on the design of tools for the analysis of HRV and repolarization intervals in unrestrained rats based on long-term ECG recordings. The program will be applied to the ECGs recorded during the current ongoing experiment to identify potential cardiac abnormalities after exposure, and will be comparable with the ECG measurements performed in the Center’s epidemiology and controlled human exposure projects.

The methods described above for HRV analysis were applied to data from a cross-over pilot study on the effects of inhaled ultrafine particles (carbon/20 percent Fe) with and without inhaled endotoxin priming. Six SHR rats (18-20 months) with radiotelemetry implants were exposed to ultrafine particles and endotoxin priming, alone and in combination, followed by ECG, body temperature, activity, and BP signal measurements in intervals through the 5th post-exposure day. Analyses have not revealed any changes in HRV associated with exposure. However, we found that the length of recording time (5 minutes) was insufficient for drawing meaningful conclusions. We presently are in the last phase of a second cross-over study in aged SH rats with continuous recording times. Data are being reanalyzed now. As a positive control, the rats of our pilot study were exposed systemically to endotoxin prior to sacrifice. Preliminary analyses suggest dramatic HRV changes in these animals. The results will be used in future experiments to: (1) target the appropriate post-exposure times for analyses; and (2) gauge the magnitude of expected changes in HRV.

The endotoxin inhalation model was used to examine the effects of ultrafine carbon/Fe particles in combination with ozone in young and old mice; separate studies were performed to assess the effect that systemic priming with endotoxin has on the response to inhaled ultrafine particles (see discussion above).

Influenza Rodent Model. Our low dose LPS inhalation model has been very useful for differentiating age-related effects of ultrafine particles in rodents. We have developed a model of influenza A virus infection in mice and rats as a priming agent for subsequent ultrafine particle exposures. The inflammatory response in the lung after intranasal instillation of the influenza virus into mice and rats was measured over several post-exposure days and compared to results obtained after intratracheal instillation. The peak of the inflammatory response in terms of appearance of PMNs in lung lavage occurs at approximately 48 hours after instillation, at which point a lymphocytic infiltration also occurs. Individual variability after intranasal instillation appears greater when compared to intratracheal instillation. Therefore, subsequent studies will be done using intratracheal instillation of influenza A. Pilot studies have been performed in influenza-primed mice and rats with additional instillation of ultrafine TiO2 particles to test the concept that influenza priming increases sensitivity to a subsequent second particulate stimulus. Results showed, indeed, that ultrafine TiO2 administered on day 2 after influenza priming caused significantly greater pulmonary inflammation than TiO2 given to unprimed animals. This model has now successfully been used with inhaled ultrafine particles as described above.

Studies With Ultrafine Particle Concentrator. We have initiated collaborative studies with the Harvard PM Center to use their ultrafine particle concentrator for exposures of our aged SH rats prepared for telemetry recordings of ECG, BP, and body temperature. First, studies were performed at Rochester, with the Harvard ultrafine concentrator in a location where air from an adjacent moderately busy road was drawn in and concentrated for animal exposures. We exposed 20-month old Fischer-344 rats for 6 hours to the concentrated ambient ultrafine particles. Since the concentrator is a prototype (first generation) model, the concentrated particles not only consisted of the ultrafine mode but there also was overlap into the fine particle mode. Figure 2 shows the number concentration of the ambient incoming aerosol and the outgoing concentrated particles. The count median diameters (CMDs) were about 35 nanometers (nm), with geometric standard deviation (GSD) of 1.9. The average particle number concentration over the 6-hour period was about 1.8 x 105 particles (p)/cm3, the incoming number concentration about 1.5 x 104 p/cm3. Four groups of rats were exposed to: (1) priming with low-dose inhaled LPS followed by filtered air; (2) priming with inhaled saline followed by filtered air; (3) priming with inhaled LPS followed by concentrated ultrafine particle exposure; and (4) priming with inhaled saline followed by concentrated ultrafine particle exposure. Animals were sacrificed on the following day. Lung lavage analysis was performed and various blood parameters were measured (blood leukocytes, fibrinogen, plasma proteins). Figure 3 shows the result of lung lavage cell analysis in terms of PMN responses and release of reactive oxygen species using PMA stimulation. Significant increases in these endpoints following concentrated ultrafine particle exposures were found. Further results are forthcoming.

Figure 2. Number Concentration of Ambient Incoming Aerosol and Outgoing Concentrate Particles

Figure 3. Lung Lavage Neutrophils 24 Hours After a 6-hour Exposure to Concentrated Ambient Ultrafine Particles in 20-Month Old Rats

Dosimetry Studies

We have developed a method to generate ultrafine 13C particles for use in rat dosimetry studies. After several methodological improvements, we performed a study to determine whether ultrafine elemental carbon particles translocate to the liver and other extrapulmonary organs following inhalation as singlet particles by rats (Oberdörster, et al. 2002). We generated ultrafine 13C particles as an aerosol with CMDs of 20-29 nm (GSD 1.7) using electric spark discharge of 13C graphite electrodes in argon. Nine Fischer-344 rats were exposed to these particles for 6 hours in whole-body inhalation chambers at concentrations of 180 and 80 µg/m3; three animals each were killed at 0.5, 18, and 24 hours post-exposure. Six unexposed rats served as controls. Lung lobes, liver, heart, brain, olfactory bulb, and kidney were excised, homogenized, and freeze-dried for analysis of the added 13C by isotope ratio mass spectrometry. Organic 13C was not detected in the 13C particles. The 13C retained in the lung at 30 minutes post-exposure was roughly 70 percent less than predicted by rat deposition models for ultrafine particles, and did not significantly change during the 24-hour post-exposure period. Normalized to exposure concentration, the added 13C per gram of lung on average in the post-exposure period was approximately 9 ng/g organ/µg/m3. Significant amounts of 13C had accumulated in the liver by 30 minute post-inhalation only at the high exposure concentration, whereas by 18 and 24 hours post-exposure the 13C concentration of the livers of all exposed rats was almost half the 13C concentration found in the lung (see Figure 4). Considering the approximately 10-fold greater weight of the liver compared to the lung, the 13C amount in the liver was ~5-fold greater than in the lung by 18 and 24 hours after exposure. No significant increase in 13C was detected in the other examined organs. These results demonstrate effective translocation of ultrafine elemental carbon particles to the liver 1 day after inhalation exposure. Potential translocation pathways include direct input into the blood compartment from ultrafine carbon particles deposited throughout the respiratory tract.

Figure 4. Lung and Liver 13C Concentration in Rats at Different Times After Exposure to Ultrafine 13C Particles, Normalized to the Exposure Concentration

In a pilot study, 13C analysis of lung and extrapulmonary organs was analyzed on day 1 and day 7 post ultrafine 13C particle exposure. Results again showed significant amounts of added 13C in the liver on day 1, but no longer on day 7. However, on day 7, significant increases in added 13C in heart, brain, and the olfactory bulb were found. This prompted us to perform a time-course study with measurement of 13C organ content on days 1, 3, 5, and 7 after a 6-hour ultrafine 13C particle exposure. Based on earlier studies in the literature reporting translocation of ultrafine organic particles along sensory nerve endings in the lung, we hypothesized that translocation of inhaled ultrafine particles occurs in the nasal compartment along the olfactory nerve into the olfactory bulb. This would explain findings of our pilot study. Results of our time-course study, indeed, showed that olfactory bulb 13C content significantly was increased on all post-exposure days, and that cerebrum and cerebellum also had increased 13C levels which were significant on days 1 and 7, and on days 1 and 5, respectively (see Figure 5).

Figure 5. Translocation of Inhaled Ultrafine 13C Particles to Tissues of the Central Nervous System Over 7 Days Post-Exposure. *Significantly increased 13C compared to control levels (P<0.05, Dunnett's Test).

Our studies performed within our PM Center's Pilot Programs used ultrafine iridium-192 (192Ir) particles. Iridium is the least soluble of metals in the lung and is, therefore, best suited to study its disposition after inhalation. Dr. Kreyling of the GSF München, is the Project Investigator of this pilot study. Dr. Kreyling's findings were in contrast to our results with ultrafine 13C particles. His results showed that after intratracheal inhalation exposure ultrafine iridium particles are not translocated to a significant degree to extrapulmonary organs (Kreyling, et al. 2002), suggesting that not only the particle size but also the material and surface properties like structure and composition may influence the amount of transportation. Differences in translocation of inhaled ultrafine particles based on their chemistry will be further investigated in a collaborative approach.

Future Activities:

Planned future studies include exposure of rodents to highway aerosols, which are freshly-generated and occur at extremely high number concentrations of up to 10 x 106 p/cm3. We plan to collaborate with Dr. D. Kittelson, University of Minnesota, on these studies, using his air-conditioned truck equipped with instruments for physico-chemical characterization of roadway aerosols. While driving this truck on Rochester highways, air is taken in through a sampling tube at the height of passenger cars, and rodents are exposed to these untreated particles/gases in whole-body exposure chambers. Filtered air exposed control animals and animals exposed to particle filtered gaseous components of the on-road aerosols serve as comparison groups.

Further studies will evaluate transport mechanisms of ultrafine particles across the alveolar epithelium and across endothelium in extrapulmonary organs, as well as neuronal transport mechanisms.


Journal Articles on this Report : 4 Displayed | Download in RIS Format

Other subproject views: All 33 publications 31 publications in selected types All 27 journal articles
Other center views: All 104 publications 98 publications in selected types All 90 journal articles
Type Citation Sub Project Document Sources
Journal Article Kreyling WG, Semmler M, Erbe F, Mayer P, Takenaka S, Schulz H, Oberdorster G, Ziesenis A. Translocation of ultrafine insoluble iridium particles from lung epithelium to extrapulmonary organs is size dependent but very low. Journal of Toxicology and Environmental Health-Part A 2002;65(20):1513-1530. R827354 (Final)
R827354C004 (2001)
R827354C004 (Final)
R832415 (2010)
R832415 (2011)
R832415 (Final)
R832415C004 (2011)
  • Abstract from PubMed
  • Abstract: Taylor and Francis-Abstract
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  • Journal Article Oberdorster G. Pulmonary effects of inhaled ultrafine particles. International Archives of Occupational and Environmental Health 2001;74(1):1-8. R827354 (Final)
    R827354C004 (2000)
    R827354C004 (2001)
    R827354C004 (Final)
    R826784 (Final)
    R832415 (2010)
    R832415 (2011)
    R832415 (Final)
    R832415C004 (2011)
  • Abstract from PubMed
  • Full-text: Precaution.org-Full Text PDF
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  • Abstract: SpringerLink-Abstract
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  • Journal Article Oberdorster G, Sharp Z, Atudorei V, Elder A, Gelein R, Lunts A, Kreyling W, Cox C. Extrapulmonary translocation of ultrafine carbon particles following whole-body inhalation exposure of rats. Journal of Toxicology and Environmental Health, Part A: Current Issues 2002;65(20):1531-1543. R827354 (Final)
    R827354C004 (2001)
    R827354C004 (Final)
    R826784 (Final)
    R832415 (2010)
    R832415 (2011)
    R832415 (Final)
    R832415C004 (2011)
  • Abstract from PubMed
  • Full-text: UMN-Full Text PDF
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  • Abstract: Taylor & Francis-Abstract
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  • Journal Article Veranth JM, Gelein R, Oberdorster G. Vaporization–condensation generation of ultrafine hydrocarbon particulate matter for inhalation toxicology studies. Aerosol Science and Technology 2003;37(7):603-609. R827354C004 (2001)
    R827354C004 (Final)
  • Full-text: Tandfonline-Full Text
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  • Abstract: Informaworld
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  • Other: Informaworld PDF
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  • Supplemental Keywords:

    animal model, dosimetry, pulmonary, cardiovascular, ultrafine carbon particle, UFP, particulate matter, PM, electrocardiogram, ECG, hypertensive, rat, heart rate variability, HRV., RFA, Health, Scientific Discipline, Air, particulate matter, Toxicology, air toxics, Environmental Chemistry, Health Risk Assessment, Risk Assessments, Biochemistry, Atmospheric Sciences, Molecular Biology/Genetics, ambient air quality, biostatistics, health effects, particle size, particulates, risk assessment, sensitive populations, cytokine production, cardiopulmonary responses, fine particles, human health effects, lung, morbidity, ambient air monitoring, ambient air, cardiovascular vulnerability, pulmonary disease, susceptible populations, animal model, ambient monitoring, particle exposure, environmental health effects, pulmonary, lung inflamation, particulate exposure, coronary artery disease, tropospheric ozone, urban air pollution, inhalation toxicology, aerosol, cardiopulmonary, mortality, human health, urban environment, aerosols, cardiovascular disease, metals, ultrafine particles

    Progress and Final Reports:

    Original Abstract
  • 1999 Progress Report
  • 2000 Progress Report
  • 2002 Progress Report
  • 2003 Progress Report
  • 2004 Progress Report
  • Final Report

  • Main Center Abstract and Reports:

    R827354    Airborne PM - Rochester PM Center

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R827354C001 Characterization of the Chemical Composition of Atmospheric Ultrafine Particles
    R827354C002 Inflammatory Responses and Cardiovascular Risk Factors in Susceptible Populations
    R827354C003 Clinical Studies of Ultrafine Particle Exposure in Susceptible Human Subjects
    R827354C004 Animal Models: Dosimetry, and Pulmonary and Cardiovascular Events
    R827354C005 Ultrafine Particle Cell Interactions: Molecular Mechanisms Leading to Altered Gene Expression
    R827354C006 Development of an Electrodynamic Quadrupole Aerosol Concentrator
    R827354C007 Kinetics of Clearance and Relocation of Insoluble Ultrafine Iridium Particles From the Rat Lung Epithelium to Extrapulmonary Organs and Tissues (Pilot Project)
    R827354C008 Ultrafine Oil Aerosol Generation for Inhalation Studies