Abstract
Previous studies have suggested that the adverse health effects from ambient particulate matter (PM) are linked to the formation of reactive oxygen species (ROS) by PM in cardiopulmonary tissues. While hydroxyl radical ((•)OH) is the most reactive of the ROS species, there are few quantitative studies of (•)OH generation from PM. Here we report on (•)OH formation from PM collected at an urban (Fresno) and rural (Westside) site in the San Joaquin Valley (SJV) of California. We quantified (•)OH in PM extracts using a cell-free, phosphate-buffered saline (PBS) solution with or without 50μM ascorbate (Asc). The results show that generally the urban Fresno PM generates much more (•)OH than the rural Westside PM. The presence of Asc at a physiologically relevant concentration in the extraction solution greatly enhances (•)OH formation from all the samples. Fine PM (PM(2.5)) generally makes more (•)OH than the corresponding coarse PM (PM(cf), i.e. with diameters of 2.5 to 10 μm) normalized by air volume collected, while the coarse PM typically generates more (•)OH normalized by PM mass. (•)OH production by SJV PM is reduced on average by (97±6)% when the transition metal chelator desferoxamine (DSF) is added to the extraction solution, indicating a dominant role of transition metals. By measuring calibration curves of (•)OH generation from copper and iron, and quantifying copper and iron concentrations in our particle extracts, we find that PBS-soluble copper is primarily responsible for (•)OH production by the SJV PM, while iron often makes a significant contribution. Extrapolating our results to expected burdens of PM-derived (•)OH in human lung lining fluid suggests that typical daily PM exposures in the San Joaquin Valley are unlikely to result in a high amount of pulmonary (•)OH, although high PM events could produce much higher levels of (•)OH, which might lead to cytotoxicity.
Highlights
Epidemiological studies have shown strong correlations between the exposure to ambient particulate matter (PM) and adverse human health outcomes such as pulmonary and cardiovascular diseases and premature deaths (Dockery et al, 1993; Pope et al, 1995, 2004; Pekkanen et al, 2002; Pope and Dockery, 2006)
Examples of OH generation from fine and coarse San results to the positive control because we found that OH Joaquin Valley particles extracted in a surrogate lung fluid containgeneration from the positive control was covariant with sam- ing 50 μM ascorbate
We can compare our initial rates of OH generation in Fresno and Westside PM extracts with values determined from southern California quasi-ultrafine PM (PM0.18), which were extracted in a pH 6.4 solution containing 500 μM Asc (DiStefano et al, 2009)
Summary
Epidemiological studies have shown strong correlations between the exposure to ambient particulate matter (PM) and adverse human health outcomes such as pulmonary and cardiovascular diseases and premature deaths (Dockery et al, 1993; Pope et al, 1995, 2004; Pekkanen et al, 2002; Pope and Dockery, 2006). These studies indicate the amounts of OH that can be chemically generated by different particles, and generally find that transition metals play the dominant role in OH generation Transition metals such as Fe and Cu are common components of PM that can produce ROS – both directly via chemical reactions and indirectly via inflammatory cell activation – causing oxidative stress, inflammation, mutagenesis and cell proliferation, which can result in cardiopulmonary diseases and cancer (Kennedy et al, 1998; Jimenez et al, 2000; Hetland et al, 2000; Prahalad et al, 1999; Ghio et al, 1999; Knaapen et al, 2002; Donaldson et al, 2003; Schaumann et al, 2004).
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