Ultrafine carbon particles: Induction of oxidative stress in lung epithelial cells

Environmental particulate air pollution (PM10) is composed of 50% carbon, it has been hypothesised that an ultrafine fraction of PM10 is responsible for its adverse health effects. We have previously demonstrated that whole PM10 has hydroxyl radical activity and, in addition, causes oxidative stress and inflammation in rat lungs after instillation. In order to elucidate the toxicity of ultrafine carbon black we compared ultrafine carbon black particles (UFCB, 10-30 nm diameter) with fine respirable carbon black particles (FCB; 100-1000 nm) for free radical activity and ability to inhibit metabolism of A549 epithelial cells in culture. The role of free radicals was investigated using the hydroxyl radical scavenger, mannitol. Using depletion of supercoiled plasmid DNA, a common measure of hydroxyl radical activity, we found that UFCB had more hydroxyl radical activity than FCB when compared at equal mass (data as mean supercoiled band intensity in 4 separate experiments):- FCB 7181; UFCB 3142 (pooled SEM 832), P<0.05. The cellular respiration of A549 cells was inhibited at 48 hours by UFCB but not by FCB:- data as mean ± SEM of MTT dye reduction in 4 separate experiments; control 0.56 ± 0.01; UFCB 0.46 ± 0.01; CB 0.59 ± 0.02 absorbance units. Mannitol prevented the inhibition of MTT dye reduction by UFCB at 48 hours (data not shown). Glutathione levels, a measure of oxidative stress, were lowered at 2 and 4 hours after treatment with UFCB but not CB (data not shown).