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The adverse health effects of air pollutants have been associated with their redox and electrophilic properties. Although the specific chemical species involved in these effects are not known, the characterization of their general physical and chemical properties is important to our understanding of the mechanisms by which they cause health problems. This manuscript describes results of a study examining the partition properties of these activities in aqueous and organic media. The water and dichloromethane (DCM) solubility of redox active and electrophilic constituents of seven diesel exhaust particle (DEP) samples were determined with assays developed earlier in this laboratory. The constituents exhibiting redox activity, which included both metals and nonmetal species, were associated with the particles in the aqueous suspensions. Portions of the redox active compounds were also DCM-soluble. In contrast, the electrophilic constituents included both water-soluble and DCM-soluble species. The role of quinones or quinone-like compounds in redox and electrophilic activities of the DCM-soluble constituents was assessed by reductive acetylation, a procedure that inactivates quinones. The results from this experiment indicated that most of the activities in the organic extract were associated with quinone-like substances. The partition properties of the reactive species are important in exposure assessment since the toxicokinetics of particles and solutes are quite distinct.

9,10-Phenanthraquinone (PQ), a component of airborne particulate matter, causes marked cellular protein oxidation and cytotoxicity through a two-electron reduction to 9,10-dihydroxyphenanthrene (PQH2), which is associated with the propagation of reactive oxygen species (K. Taguchi et al., Free Radic. Biol. Med. 43:789-799, 2007). In the present study, we explored a biotransformation pathway for the detoxification of PQ. Exposure of human pulmonary epithelial A549 cells to PQ resulted in a time-dependent appearance of an unknown metabolite in the medium that was identified as the monoglucuronide of PQH2 (PQHG). Whereas a variety of isozymes of uridine 5'-diphosphate glucuronosyltransferase (UGTs) are responsible for PQHG formation, UGT1A10 and UGT1A6 were particularly effective catalysts for glucuronide conjugation. In cell-free systems, PQ exhibited a rapid thiol oxidation and subsequent oxygen consumption in the presence of dithiothreitol, whereas PQHG did not. Unlike the parent compound, PQHG completely lost the ability to oxidize cellular proteins and cause cell death in A549 cells. In addition, deletion of the transcription factor Nrf2 decreased PQHG formation and increased PQ-mediated toxicity of mouse primary hepatocytes. Thus, we conclude that PQHG is a metabolite of PQ, generated through PQH2, that terminates its redox cycling and transports it to extracellular space.

Quinones are widely used as medicines or redox agents. The chemical properties are based on the reactions against an electron donor. 9,10-Phenanthraquinone (PQ), which is a quinone contaminated in airborne particulate matters, forms redox cycling, not Michael addition, with electron donors. Redox cycling of PQ contributes to its toxicity, following generation of reactive oxygen species (ROS). Detoxification of quinones is generally thought to be two-electron reduction forming hydroquinones. However, a hydroquinone of PQ, 9,10-dihydroxyphenanthrene (PQH(2)), has been never detected itself, because it is quite unstable. In this paper, we succeeded in detecting PQH(2) as its stable derivative, 9,10-diacetoxyphenanthrene (DAP). However, higher concentrations of PQ (>4 microM) form disproportionately with PQH(2), producing the 9,10-phenanthraquinone radical (PQ(-)) which is a one-electron reducing product of PQ. In cellular experiments using DAP as a precursor of PQH(2), it was shown that PQH(2) plays a critical role in the oxidative protein damage and cellular toxicity of PQ, showing that two-electron reduction of PQ can also initiate redox cycling to cause oxidative stress-dependent cytotoxicity.

The potential adverse health effects of PM2.5(particulate matter with an aerodynamic diameter <2.5 μm) and vapor samples from three communities that neighbor railyards, Commerce (CM), Long Beach (LB), and San Bernardino (SB), were assessed by determination of chemical reactivities attributed to the induction of oxidative stress by air pollutants. The assays used were dithiothreitol (DTT)- and dihydrobenzoic acid (DHBA)-based procedures for prooxidant content and a glyceraldehyde-3-phosphate dehydrogenase (GAPDH) assay for electrophiles. Prooxidants and electrophiles have been proposed as the reactive chemical species responsible for the induction of oxidative stress by air pollution mixtures. The PM2.5samples from CM and LB sites showed seasonal differences in reactivities, with higher levels in the winter, whereas the SB sample differences were reversed. The reactivities in the vapor samples were all very similar, except for the summer SB samples, which contained higher levels of both prooxidants and electrophiles. The results suggest that the observed reactivities reflect general geographical differences rather than direct effects of the railyards. Distributional differences in reactivities were also observed, with PM2.5fractions containing most of the prooxidants (74–81%) and the vapor phase most of the electrophiles (82–96%). The high levels of the vapor-phase electrophiles and their potential for adverse biological effects point out the importance of the vapor phase in assessing the potential health effects of ambient air. Implications: PM2.5 and its corresponding vapor phase, containing semivolatile organics, were collected in three communities in the Los Angeles Basin and examined with toxicologically relevant chemical assays. The PM2.5 phase contained most of the prooxidants and the vapor phase contained most of the electrophiles, whose content was highest in summer samples from a receptor site that reflected greater photochemical processing of the air parcel during its transport. As electrophiles initiate both adverse and adaptive responses to foreign substances by biological systems, their presence in the vapor phase emphasizes the importance of this phase in the overall health effects of ambient air. [ABSTRACT FROM AUTHOR]

Many of the adverse health effects of airborne particulate matter (PM) have been attributed to the chemical properties of some of the large number of chemical species present in PM. Some PM component chemicals are capable of generating reactive oxygen species and eliciting a state of oxidative stress. In addition, however, PM can contain chemical species that elicit their effects through covalent bond formation with nucleophilic functions in the cell. In this manuscript, we report the presence of constituents with electrophilic properties in ambient and diesel exhaust particles, demonstrated by their ability to inhibit the thiol enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAPDH). GAPDH is irreversibly inactivated by electrophiles under anaerobic conditions by covalent bond formation. This inactivation can be blocked by the prior addition of a high concentration of dithiothreitol (DTT) as an alternate nucleophile. Addition of DTT after the reaction between the electrophile and GAPDH, however, does not reverse the inactivation. This property has been utilized to develop a procedure that provides a quantitative measure of electrophiles present in samples of ambient particles collected in the Los Angeles Basin and in diesel exhaust particles. The toxicity of electrophiles is the result of irreversible changes in biological molecules; recovery is dependent on resynthesis. If the resynthesis is slow, the irreversible effects can be cumulative and manifest themselves after chronic exposure to low levels of electrophiles. [Copyright &y& Elsevier]