Enhancement of 2 '-deoxyguanosine hydroxylation and DNA damage by coal andoil fly ash in relation to particulate metal content and availability

Epidemiologic studies have shown causal relationships between air pollution particles and adverse health effects in susceptible subpopulations. Fly as h particles (containing water-soluble and insoluble metals) are a component of ambient air particulate pollution and may contribute to particulate-ind uced health, effects. Some of the pathological effects after inhalation of the particles may be due to reactive oxygen species (ROS) produced by metal -catalyzed reactions. In this investigation, we analyzed emission source pa rticulates oil fly ash (OFA) and coal fly ash (CFA) for metal content and s olubility in relation to their ability to induce 2'-deoxyguanosine (dG) hyd roxylation and DNA damage as measured by 8-oxo-dG formation by HPLC/UV-elec trochemical detection (ECD). Water-soluble vanadium and nickel were present at the highest concentrations, and iron was present in trace amounts in OF A (5.1% V, 1.0% Ni, and 0.4% Fe by weight), In contrast, CFA comprised most ly of water-insoluble aluminosilicates and iron (9.2% Al, 12.2% Si, and 2.8 % Fe by weight). As a first approach to gain insight into the mode of actio n of these particulates, we examined metal species-catalyzed kinetics of dG hydroxylation. Metal species at a concentration of 0.1 mM in the incubatio n mixture containing 0.1 mM dG under ambient air at room temperature cataly zed maximum 8-oxo-dG formation at 15 min with yields ranging from 0.05 to 0 .17%, decreasing in the following order: vanadium(IV) > iron(II) > vanadium (V) > iron(III) greater than or equal to nickel(II). Insoluble Fe(III) oxid e (Fe2O3) under similar conditions had no effect. Consistent with these res ults, OFA rich in vanadium and nickel concentrations showed a dose-dependen t increase in the level of dG hydroxylation to 8-oxo-dG; formation at parti culate concentrations of 0.1-1 mg/mL (p < 0.05). In contrast, CFA with high concentrations of aluminosilicates and iron did not result in a significan t increase in the level of 8-oxo-dG over that of the control, i.e., dG (p > 0.05). DMSO, a (OH)-O-. scavenger, inhibited OFA-induced 8-oxo-dG formatio n, and metal ion chelators, deferoxamine (DFX), DTPA, and ferrozine blocked OFA-induced 8-oxo-dG formation. OFA and CFA induced 8-oxo-dG formation in a pattern similar to that observed for dG hydroxylation when calf thymus DN A was used as a substrate. Treatment of OFA particles with DFX before react ing with DNA or addition of a catalase in the incubation mixture significan tly suppressed 8-oxo-dG formation (p < 0.05). These results suggest that me tal availability, but not the concentration of metals present in CFA and OF A, is critical in mediating molecular oxygen-dependent dG; hydroxylation an d DNA base damage.