2006 Progress Report: The Chemical Properties of PM and their Toxicological ImplicationsEPA Grant Number: R832413C003
Subproject: this is subproject number 003 , established and managed by the Center Director under grant R832413
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: Southern California Particle Center
Center Director: Froines, John R.
Title: The Chemical Properties of PM and their Toxicological Implications
Investigators: Cho, Arthur K. , Froines, John R. , Miguel, Antonio , Kumagai, Yoshito
Current Investigators: Cho, Arthur K. , Froines, John R. , Harkema, Jack , Fukuto, Jon , Kumagai, Yoshito
Institution: University of California - Los Angeles , University of Tsukuba
Current Institution: University of California - Los Angeles , Michigan State University , University of Tsukuba
EPA Project Officer: Chung, Serena
Project Period: October 1, 2005 through September 30, 2010 (Extended to September 30, 2012)
Project Period Covered by this Report: October 1, 2005 through September 30, 2006
RFA: Particulate Matter Research Centers (2004) RFA Text | Recipients Lists
Research Category: Health Effects , Air
The overall objective of Project 3 is to characterize the chemical properties of particulate matter (PM) from a variety of PM sources, with a focus on their potential to induce redox chemistry and oxidative stress in biological tissues. This project is testing the hypothesis that PM contains reactive chemical species and they, either separately or as a mixture, are responsible for the toxicological phenomenon associated with PM. These chemical species can be organic or inorganic and act through several possible chemical reactions with biological substrates. We are focusing on two general mechanisms, redox and electrophilic reactions. Redox reactions involve the catalytic reduction of oxygen to reactive oxygen species by components of PM with electrons from biological sources. In the electrophilic reactions, a reactive function in PM reacts with nucleophilic functions in biological systems from covalent bonds. These bonds are irreversible, so that the affected biological molecule is destroyed. The thiol group is a likely target of the two reactions, as this group participates in both redox and covalent bond forming reactions. Thiols serve key functions in proteins such as enzymes, transporters, and receptors so their modification can result in substantial disruption of cell biochemistry. By characterizing and quantitatively determining the reactivity in a given PM sample with respect to these chemical properties, we hope to be able to predict its potential toxicity.
Electrophilic Chemistry and PM Constituents
1,2-Naphthoquinone (1,2-NQ) has recently been identified as an environmental quinone in diesel exhaust particles (DEP) and atmospheric PM2.5. We have found that this quinone is capable of causing a concentration-dependent contraction of tracheal smooth muscle in guinea pigs with EC50 value of 18.7 μM. The contraction required extracellular calcium and was suppressed by L-type calcium channel blockers nifedipine and diltiazem. It was found that 1,2-NQ activated phospholipase A2 (PLA2)/lipoxygenase (LO)/vanilloid receptor (VR1) signaling. Additionally, 1,2-NQ was capable of transactivating protein tyrosine kinases (PTKs) such as epidermal growth factor receptor (EGFR) in guinea pig trachea, suggesting that phosphorylation of PTKs contributes to 1,2-NQ-induced tracheal contraction. Consistent with this notion, this action was blocked by the PTKs inhibitor genistein and the EGFR antagonist PD153035, indicating that contraction was, at least in part, attributable to PTKs phosphorylation that activates VR1, resulting in increased intracellular calcium content in the smooth muscle cells. These results demonstrate another process that could account for the toxicity of PM. Quinones of certain structures are able to bind to thiol containing proteins and irreversibly inactivate them. In contrast to the reversible effects, these actions would be cumulative over time, dependent on protein turnover for recovery resulting in significant effects occurring over time at low levels of exposure.
Chemical Assays To Identify ROS Formation in Project 4
We hypothesize that airway inflammation and deposition of airborne ultrafine particles could lead to an increase in thrombogenic and inflammatory activity in the blood, and to a disturbance in cardiovascular function. This is expected to increase the risk of adverse cardiovascular outcomes. To examine this hypothesis, we are conducting a panel study involving repeated measures of cardiovascular and inflammatory outcomes in relation to personal and micro-environmental exposures to PM air pollution. We are addressing the following specific aim in Project 3:
“to examine the relationship of cardiovascular outcomes to the production of reactive oxygen species (ROS) by PM using in vitro bioassays of concentrated particle suspensions collected at indoor sites during 5-day exposure periods.”
The assays developed in our laboratories are based on the ability of PM to transfer electrons from DTT to oxygen. This assay is a quantitative measure of redox properties. The DTT based redox activity is due primarily to organic species, but metal ions, particularly from transition metals, also contribute to redox activity. To address this component, we measured the ability of the sample to generate the Fenton chemistry product of salicylate, dihydroxybenzoic acid (DHBA), that is, the hydroxyl radical. These two assays are complementary.
A wide range of samples have been collected both indoor and outdoor during the first year of the PM Center, and DTT and DHBA determinations have been completed. The data is currently under analysis.
Study of Quinones in 5 Sites Along the Wind Trajectory of the Los Angeles Basin
In a study examining changes in air mass content, collections were made in five sites along the wind trajectory of the Los Angeles Basin on each of four days. The study focused on changes in the atmosphere as the air mass moved from the west end of the Los Angeles Basin (Santa Monica) to the east, sequentially in Long Beach, Anaheim, Mira Loma, and Riverside on each of four days. The collections were made with a Tisch sampler, using Teflon filters and a XAD resin bed for the volatile fraction. The sampler was sequentially moved along the trajectory on each day. When collected in this protocol, differences between locations were discernable in spite of the day to day variability in the concentrations. The hypothesis was that Santa Monica is primarily a source site, in which direct emissions from vehicular traffic are introduced into the air mass which can then undergo photochemical transformations as it moves eastward. The concentrations of the four quinones in the filter (PM2.5) and the volatile (XAD) fractions were determined according to an established SCPC protocol (Cho, et al., 2004) and are shown graphically in Figure 1.
Figure 1. Quinone Concentrations in the Los Angeles Basin
These results demonstrate that the quinones measured are present in both vapor and particle phases, with higher concentrations of the naphthoquinones in the vapor phase. This finding implies that exposure and toxic properties associated with these compounds must be assessed taking both phases into account. Together with prior SCPC results obtained from sampling in the Caldecott Tunnel, the findings are consistent with the following chemical transformations:
- 9,10-Anthraquinone (9,10-AQ) is present as direct exhaust and does not appear to increase as the air mass moves east, so it may not be a major product of photochemical transformations.
- The 9,10-PQ present in the ambient PM2.5 increases as the air mass moves east, suggesting that it is being formed by photochemical reactions. SCPC determined levels of its precursor, phenanthrene: they were highest in Santa Monica and decreased as the air mass moved east (data not shown).
- Similar arguments apply to 1,4-NQ which is found as direct exhaust but also increases in the volatile fraction as the air mass moves east. SCPC studies show that the precursor hydrocarbon, naphthalene, is present in the highest concentration of all PAHs in ambient air, constituting 95% of the total PAH content (Eiguren-Ferndanez, et al., 2004).
- 1,2-NQ levels do not appear to change with easterly movement of the air mass, but its presence in both tunnel and ambient air samples is consistent with its formation from exhaust and rapid decomposition. This is a reactive quinone, and its levels may decline rapidly with time.
- 9,10-Anthraquinone may serve as a marker for vehicular traffic. It is present in all samples and does not follow the photochemical increase associated with 1,4-NQ and 9,10-PQ.
The wide variability between days at the same location could be due to variation in traffic density or fuel sources, but the trends of the mean values are consistent with our hypotheses regarding generation of some reactive compounds by sources and subsequent photochemical changes, i.e., low levels of photochemical products at sources and higher levels at receptors. The increase in several quinone concentrations observed as the air mass proceeds to the receptor sites, suggests that adverse health effects associated with this class of reactive organic compound will also increase.
We are currently analyzing samples collected under Project 1 of this report at the 710 freeway in Los Angeles, and as part of the Project 4 study of retirement homes, using assays for redox activity. We are finalizing the protocol for our GAPDH assay, for application to ambient particle samples. These activities will be completed in the remainder of Year 1. Chemical toxicology assays (DTT and DHBA) will be carried out to address the requirements of the Year 2 sampling campaign. Year 2 will include the analysis of particle and vapor phase samples collected by Dr. William Hinds. Collections will be made while traveling on a freeway, at a non-freeway source site and at a receptor site impacted by photochemically aged air masses.
Cho AK, DiStefano E, You Y, Rodriquez CE, Schmitz DA, Kumagai Y, Miguel AH, Eiguren-Fernandez A, Kobayashi T, Avol E, Froines JR. Determination of four quinones in diesel exhaust particles, SRM 1649a and atmospheric PM2.5. Aerosol Science and Technology 2004;38(S1):68-81.
Eiguren-Fernandez A, Miguel AH, Froines JR, Thurairatnam A, Avol EL. Seasonal and spatial variation of polycyclic aromatic hydrocarbons in vapor-phase and PM2.5 in Southern California urban and rural communities. Aerosol Science and Technology 2004;38:447–455.
Journal Articles:No journal articles submitted with this report: View all 47 publications for this subproject
Supplemental Keywords:bioavailability, metabolism, chemicals, oxidation-reduction, biochemistry, ambient air, particulate matter, oxidative stress,, RFA, Health, Scientific Discipline, Air, particulate matter, Health Risk Assessment, Risk Assessments, Biochemistry, Ecology and Ecosystems, particulates, atmospheric particulate matter, chemical assys, particle matrix, chemical characteristics, human health effects, PM 2.5, toxicology, airway disease, cardiovascular vulnerability, airborne particulate matter, air pollution, human exposure, vascular dysfunction, cardiovascular disease, human health risk
Progress and Final Reports:Original Abstract
Main Center Abstract and Reports:R832413 Southern California Particle Center
Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R832413C001 Contribution of Primary and Secondary PM Sources to Exposure & Evaluation of Their Relative Toxicity
R832413C002 Project 2: The Role of Oxidative Stress in PM-induced Adverse Health Effects
R832413C003 The Chemical Properties of PM and their Toxicological Implications
R832413C004 Oxidative Stress Responses to PM Exposure in Elderly Individuals With Coronary Heart Disease
R832413C005 Ultrafine Particles on and Near Freeways