Inherent Redox Properties of Diesel Exhaust Particles: Catalysis of the Generation of Reactive Oxygen Species by Biological Reductants

Abstract

The toxicity of diesel exhaust particles (DEP) can be due to the particle itself, extractable components, or both. Many studies focus on the biological properties of DEP-extractable components although it is possible that chemical properties inherent to the DEP itself can lead to toxicity. Thus, an examination of the chemistry inherent to DEP was carried out. Herein, we report that DEP are capable of catalyzing the consumption of O2 (monitored using a Clarke electrode) by ascorbate and thiols leading to the generation of reactive oxygen species. Consistent with the idea that DEP are capable of catalyzing the generation of reactive oxygen species, they were also found to catalyze DNA strand breakage via an O2- and reductant-dependent process. Significantly, extraction of DEP with either organic solvent (methylene chloride) or acid (aqueous HCl) did little to abrogate this chemistry. Finally, using electron paramagnetic spectrometry (EPR), DEP were found to have paramagnetic properties. The paramagnetic character of DEP may be important to their ability to catalyze the formation of reactive oxygen species and at least partially responsible for their toxicity. These findings indicate that studies that primarily consider or examine particle extracts as the toxic components of DEP may be insufficient in describing the toxicity associated with DEP exposure.

Mutagenicity of diesel exhaust particles mediated by cell–particle interaction in mammalian cells

“…The observation is consistent with the findings that blocking of cellular phagocytosis with cytochalasin B or ammonium chloride dramatically reduced the mutagenicity of DEPs in mammalian cells. There is evidence to show that reactive oxygen species, including superoxide anions (O 2 − ) and hydroxyl radicals (OH • ), are generated not only from redox reactions catalyzed on the particles but also from the process of phagocytosis of particles in various cells such as alveolar macrophage and bronchial epithelial cells (Pan et al, 2004;Li et al, 2002). These biologically reactive oxyradicals may act directly or indirectly to damage neighboring biomolecules, such as DNA and membrane lipid, leading to a broad spectrum of mutations in mammalian cells (Knaapen et al, 2004).…”

Quantitative Aspects of the Interfacial Catalytic Oxidation of Dithiothreitol by Dissolved Oxygen in the Presence of Carbon Nanoparticles

“…55 The insoluble black carbon core, corresponding to aromatic amorphous or graphene structures, might also present additional DTT reactivity. 8,9,56 Depending on the defects present on such graphene structures, different amount of oxygen can be incorporated, 57 possibly as carbonyl surface functional groups which may be able to catalytically and reversibly transfer electrons from DTT to O 2 in redox reactions. Such carbonyl functions on aromatic graphene structures (vinylog) are exemplified in Figure 5.…”

“…[4][5][6] Such processes have often been reported for acellular assays involving ambient particles and occurring in a reducing environment containing molecular oxygen. [7][8][9] By definition, a heterogeneous catalyst consists of a solid which will modify the reaction kinetics between two reactants, without being consumed itself and thus changing the global stoichiometry. Two main features are noteworthy: 1.…”

Effects of a nanoceria fuel additive on the physicochemical properties of diesel exhaust particles

“…Given that these physicochemical properties are important determinants of particle toxicity, it is anticipated that using nanoceria additives to diesel fuel would alter the toxicity of the emitted DEP in various ways. 22,40,43 For example, the increased organized structure and decreased oxidative potential might decrease the bioreactivity of DEP, while reduced particle size may increase the diffusion rate of particles within and across the lung and decrease clearance rate in the lung, thereby increasing overall bioreactivity and toxicity. 27,44 Hence, the impact on the overall DEP bioreactivity and toxicity is hard to predict solely based on physiochemical property changes observed in the present study.…”

“…40 The potency of ROS generation can be assessed using simple, chemistry-based methods. For example, as a surrogate of ROS generation potency, oxidative potentials of the DEPs and two reference materials were determined here through a redox-based assay called the ascorbate depletion test.…”