Ambient particulate matter induces oxidative DNA damage in lung epithelialcells

Although epidemiological studies have established a correlation between PM1 0 levels and acute cardiovascular and respiratory complications, hardly any data is available on possible chronic effects such as cancer. The purpose of this study was to investigate the production of free radicals by ambient particulate matter (TSP) and to link these data to oxidative DNA damage in lung epithelial cells. In line with previous findings oil PM10, supercoile d plasmid DNA was depleted by TSP as well as TSP supernatant (p < .001) and this effect was reduced in the presence of mannitol (5 mM). Using electron spin resonance (ESR) and the spin trap dimethyl-1-pyrroline N-oxide (DMPO) we were able to show that hydroxyl radicals ((OH)-O-.) are formed from bot h TSP and TSP supernatant. The DMPO-OH signal was completely abrogated when TSP was preincubated with deferoxamine (5 mM), showing the importance of i ron and other soluble metals in this process. Atomic absorption spectroscop y (AAS) analysis of the TSP supernatant showed the presence of soluble Fe, V: and Ni (respectively 253.0, 14.7, and 76.0 mu g/g insoluble TSP). To inv estigate the biological significance of (OH)-O-. formation by TSP 8-hydroxy deoxyguanosine (8-oxodG) was measured in a rat type II cell line by immunoc ytochemistry. The formation of ih is hydroxyl-radical-specific DNA adduct w as increased twofold (p < .01) after incubation with TSP supernatants, and this effect was inhibited by deferoxamine (p <.01). In summary our results provide direct evidence that ambient particulate matter generates hydroxyl radicals in acellular systems. Furthermore, we showed that these particulat es induce the hydroxyl-radical-specific DNA lesion 8-oxodG in lung target c ells via an iron-mediated mechanism.