Differential effect of residual oil fly ash (ROFA), ambient particulate matter and diesel exhaust particle (DEP) on the human pulmonary alveolar epithelium

Epidemiological studies have shown that exposure to particulate matter (PM) contributes to cardiopulmonary morbidity and mortality. Evidence suggests that the diesel exhaust in ambient air in major cities mediates a significant proportion of the adverse health effects. However, it has been speculated that these effects might be increased in cities within the oil and gas producing countries as a result of a combined effect of inhaling both diesel exhaust particles (DEP) and residual oil fly ash (ROFA) It is hypothesised that the nature and degree of alveolar epithelial reactivity will depend on the physico-chemistry of the particles, and that DEP/ROFA mixture will result in greater bio-reactivity compared to the same amount of DEP and ROFA alone. The specific aim is to determine the physico-chemical characteristics of ambient PM, DEP, ROFA and DEP/ROFA mixture and to compare their cellular reactivity/effects on human alveolar epithelium in vitro. The physico-chemical composition of the particles was determined using transmission electron microscope and energy dispersive x-ray spectrometer (TEM/EDX) analysis. Primary human alveolar type 2 epithelial cells (AT2) and a transformed human alveolar type 1 (TT1) epithelial cell line were exposed to ambient particles, ROFA, DEP and a ROFA/ DEP (1:1) mixture. Reactive oxygen species (ROS) production and cell viability were evaluated using the dichlorofluorescin (DCFDA) and 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium (MTT) assay respectively. Enzyme-linked immunosorbent assay (ELISA) was used to quantify release of CXCL8, IL-6, and CCL2. TEM/EDX results revealed that transition metals and other reactive elements were present in the samples. The result also showed that ambient PM has an amorphous structure which made particle size difficult to determine. The estimated average diameters of ROFA and DEP were 74 ±17nm and 65 ± 2nm respectively. When mixed, it was 76 ± 24nm. Morphologically, these particles have large spherical, agglomerate and crystalline structures. Cellular exposures to PM were associated with significant increases in cytokine and chemokine release compared to non-treated controls (P< 0.002). At high concentrations (50 and 100μg/ml) the ROFA/DEP mixtures caused a significant increase in IL-6, CXCL8, and CCL2 release by TT-1 cells compared to exposure to an equivalent amount of DEP or ROFA alone (P