Short-term exposures to US EPA-regulated atmospheric particulate matter (PM) air pollution with diameters <2.5 um (PM2.5) and <10 um (PM10), have been associated with acute increases in cardiovascular hospitalization and mortality. However, the causative chemical components and underlying pathophysiological mechanisms remain to be clarified. Toxicological data suggest pro-oxidant PM chemical species from fossil fuel combustion are causative factors in oxidative stress, inflammation, thrombosis, and vascular dysfunction, which have the potential to precipitate adverse events such as myocardial infarction. Our overall objective is to chemically characterize particle exposures and relate these exposures to interrelated health outcomes in a cohort of potentially susceptible elderly subjects. We will evaluate within-subject exposure-response relations using 12 weekly repeated measures in each of 120 subjects living in the Los Angeles Basin. Outcomes to be measured include systemic biomarkers of oxidative stress and inflammation in the blood, airway inflammation, endothelial dysfunction, blood pressure, and whole blood gene expression (>31,000 genes), focusing on genes in biological pathways relevant to cardiovascular disease. Our overarching hypothesis is that subject health outcomes will be associated with exposure to ultrafine PM (PM<0.1 um), to organic aerosols from fossil fuel combustion, and to the overall oxidative potential of PM exposures. We further hypothesize that these PM characteristics will be linked to vehicular traffic sources, and that we will find weaker associations with PM2.5 and PM10 mass. This hypothesis is based on observations that chemicals with oxidative potential and high toxicity make up a small and highly variable fraction of PM2.5, but comprise a much greater proportion of unregulated ultrafine PM mass in areas near traffic sources. We will test our hypotheses with the following three aims: 1. Assess relations between air pollution exposures and genome-wide gene expression in peripheral blood. 2. Evaluate relations of air pollution exposures to systemic and airway biomarkers of oxidative stress and inflammation. We anticipate that different pollutant components will affect airway vs. systemic inflammation. 3. Examine relations of air pollution exposures to peripheral endothelial function and blood pressure. This will be among the first human transcriptomic studies to evaluate relations between repeated gene expression responses and chemically-characterized ambient air pollution. Our proposed assessment of the estimated effects of PM oxidative potential and toxic chemical components on combined genetic, biomarker, and physiologic outcomes offers a novel approach to air pollution research in populations. The investigation of pathophysiological responses to particle exposures (characterized by size, toxicity and source) challenges and advances existing approaches. Results will inform regulatory decisions aimed at protecting sensitive populations because putative causative constituents of PM are not well-represented by PM2.5 or PM10.
This study would be among the first using repeated measurements to analyze the relation between chemically characterized air pollutants and genome-wide gene expression patterns in peripheral blood cells from a high- risk population of elderly individuals. Gene expression results will be compared with analyses of the relation of air pollutants to vascular function and to biochemical markers of oxidative stress and inflammation in the blood and lungs. This study will contribute to the knowledge and methods needed to establish exposure limits to protect the public's health because the study aims address unresolved questions about which chemical components and sources of air pollution that have the greatest potential for toxicity in the lungs and systemically.
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