| This dissertation set out to develop and understanding of what makes individuals with pre-existing pulmonary inflammatory diseases more susceptible to particulate matter (PM) air pollutant exposure. The data presented here describes (1) the development of an in vitro system that models the epithelial inflammatory microenvironment in inflammatory lung diseases, (2) the differential cellular effects of pulmonary epithelial exposure to traffic related PM in the setting of health or an "inflammation", and (3) the contributing mechanism(s) involved in these differential cellular effects.;Pulmonary epithelial cells are exposed to both inhaled PM and pro-inflammatory mediators, and thus are appropriate to investigate the effects of PM exposure. First, an in vitro model of pulmonary epitheail cells grown in a inflammatory microenvironment was created. Primary mouse tracheal epithelial (MTE) cells grown at an air-liquid interface characteristic of the conducting airways, and LA-4 epithelial cells characteristic of alveolar type II cells were exposed to pro-inflammatory cytokines (cytomix: TNFalpha + IL-1beta + IFNgamma). Cytomix treatment of MTE and LA-4 cells resulted in increased release of neutrophillic (MIP-2) and eosinophillic (RANTES) chemokines 24 hr after treatment. Cytomix treatment of LA-4 cells resulted in increased mRNA and protein of iNOS, with the subsequent release of nitric oxide (NO), a reactive oxygen species (ROS) involved in inflammation.;Using this in vitro model, the differential effects of PM exposure were evaluated and compared to normal cells. Control and cytokine-treated LA-4 and MTE cells were exposed to diesel exhaust particles (DEP), abundantly present in urban environments and rich in organic carbon, as well as particles with low (SRM 2975) or no (carbon black) organic carbon content. Exposure of control and cytokine-treated MTE cells to DEP (20 microg/cm2; 24 hr) was seemingly without effect on cell injury (LDH release) and antioxidant status (GSH). However, exposure of inflamed MTE cells resulted in increased epithelial solute permeability. LA-4 cells exposed to DEP (25 microg/cm 2; 24 hr) induced adaptive cytoprotective (HO-1), antioxidant (GSH) responses with no apparent cell injury (LDH). In contrast, DEP exposure of cytokine-treated LA-4 cells resulted in oxidative stress culminating in significant cytotoxicity that was seemingly related to the organic carbon fraction of the particles, with particles with little or no organic carbon eliciting no significant changes.;To further investigate the oxidative stress elicited in cytokine-treated LA-4 cells exposed to DEP, the generation of the ROS superoxide (O2 ·-) was evaluated, as well as its ability to cooperate with NO to form peroxynitrite (ONOO-), a more potent radical involved in cell injury. LA-4 cells exposed to DEP (25 microg/cm 2, 24 hr) resulted in ROS production, including O2·- . However, DEP exposure of cytokine-treated LA-4 cells resulted in even greater ROS production that could be inhibited with an iNOS inhibitor (1400W) and an O2·- antioxidant (SOD). The resulting cell injury of cytokine-treated LA-4 cells exposed to DEP could be reduced by treatment with FeTMPyP, an ONOO- scavenger. Furthermore, in vivo pulmonary administration of pro-inflammatory cytokines followed by DEP inhalation resulted in increased ROS production that was effectively abrogated by treatment with FeTMPyP.;Collectively, these findings show that cytokine-treated lung epithelial cells are more susceptible to the damaging effects of organic rich DEP exposure through the cooperative effects of NO and O2·-. Whereas multiple processes may be involved in the adverse health effects of PM exposure in susceptible populations, the above mechanism may contribute to the adverse health effects of DEP exposure of individuals with chronic inflammatory lung diseases. |
