PARTICULATE MATTER INFLAMMATION AND RECEPTOR SENSITIVITY ARE TARGET CELL SPECIFIC

Abstract

The complexity of primary source particulate matter (PM) and the various cell types encountered by its inhalation raise the possibility that target cells are differentially activated. Since epithelial cells, which line the nasal-tracheal-bronchial airways, and sensory C fibers, which terminate throughout this epithelial layer, are initially targeted by inhaled PM, we compared their relative biological response in vitro to PM originating from volcanic (MSH), anthropogenic (diesel), residential (woodstove), urban ambient (St. Louis, Ottawa), and industrial emission (coal fly ash, CFA; residual oil fly ash, ROFA; oil fly ash, OFA) sources. Increases in intracellular calcium (i.e., [Ca 2+] i) are a second-messenger event that indicates cellular activation and signal transduction, in both nerve and epithelial cells. Single-cell calcium imaging recordings were taken of human bronchial epithelial cells (BEAS-2B) exposed to selected PM (50 µg/ml or 30 µg/cm 2) . These cells responded with variable increases in [Ca 2+] i ranging from abrupt increases, which returned to baseline upon washing of the cells, to oscillations of the [Ca 2+] i that did not wash out. Increases in [Ca 2+] i and inflammatory cytokine (i.e., interleukin 6, IL-6) release were measured in populations of BEAS-2B cells exposed to PM (50 µg/ml) and were shown to significantly correlate (r 2 = .80). BEAS-2B cells, stained histochemically with cobalt, displayed a concentration-dependent precipitation in response to acid pH and capsaicin, indicating the presence of acid-sensitive pathways (e.g., VR1 and acid-sensitive receptors). To demonstrate the relevance of these pathways to inflammatory cytokine (i.e., IL-6) release, BEAS-2B cells were pretreated (15 min) with antagonists to the vanilloid (VR1) receptor (i.e., capsazepine, CPZ) or acid-sensitive pathways (i.e., amiloride) before their exposure to the selected PM. A significant reduction of IL-6 release occurred in response to all PM, except for MSH and diesel exhaust. Dorsal root ganglia (DRG), which innervate the tracheal airways, were dissociated from fetal mice and pretreated with CPZ or amiloride before exposure (4 h) to the selected PM (50 µg/ml). Overall, significantly higher release occurred in PM-exposed sensory neurons relative to that of BEAS-2B epithelial cells. Although both CPZ and amiloride significantly reduced IL-6 release for all PM, the degree of inhibition was less for the PM-exposed DRG relative to BEAS-2B cells. These data show that differential increases in [Ca 2+] i; and IL-6 release occur in BEAS-2B epithelial cells and DRG sensory neurons, when exposed to PM derived from different sources. The degree of this activation, however, depends not only on the source of the PM, but also on its cellular target. This differential sensitivity of target cells may contribute to the organism's overall inflammatory response to PM exposure.