The role of oxidative stress in the prolonged inhibitory effect of ultrafine carbon black on epithelial cell function

Respired ultrafine particles induce a greater inflammation in rat lungs tha n fine particles; we have hypothesized that this is due to their comparativ ely huge number and surface area for the production of free radicals. We te sted this hypothesis by studying the effects of fine and ultrafine (uf) car bon black (CB) particles in comparison with quartz on A549 human type II al veolar epithelial cells, particularly with respect to the oxidative propert ies of these particles. Treatment with fine CB (diameter 260 nm), and quart z (up to 0.78 mu g/mm(2)) for 24 hours significantly (P < 0.05) decreased t he A549 cells metabolic competence, as measured by the ability to reduce MT T to a formazan product. The inhibitory effects of uf CB only became signif icantly different (P < 0.05) relative to the control at 48 hours, by which time the effects of fine CB and quartz were no longer significant. The inhi bition of MTT reduction by uf CB was prevented by the hydroxyl radical scav enger mannitol (2mM). In addition, measurement of reactive oxygen species p roduction using supercoiled plasmid DNA showed that uf CB exhibited signifi cantly more free radical activity than fine CB (P < 0.05). In the absence o f serum, uf CB depleted reduced glutathione at 6 hours (P < 0.008). In cont rast, CB did not significantly alter reduced or oxidized glutathione. Hence , compared with fine CB, uf CB exhibited greater free radical activity, gre ater inhibition of the reduction of MTT at 48 hours (prevented by mannitol) and a depletion of reduced glutathione. These results suggest that uf CB i nduces a greater oxidative stress than fine CB, and that this may play a ro le in the toxicological effects of this ultrafine particle. (C) 1998 Elsevi er Science Ltd. All rights reserved.