Abstract
Exposure to air pollution resulting from fossil fuel combustion has been linked to multiple short-term and long term health effects. In a previous study, exposure of lung epithelial cells to engine exhaust from heavy fuel oil (HFO) and diesel fuel (DF), two of the main fuels used in marine engines, led to an increased regulation of several pathways associated with adverse cellular effects, including pro-inflammatory pathways. In addition, DF exhaust exposure was shown to have a wider response on multiple cellular regulatory levels compared to HFO emissions, suggesting a potentially higher toxicity of DF emissions over HFO. In order to further understand these effects, as well as to validate these findings in another cell line, we investigated macrophages under the same conditions as a more inflammation-relevant model. An air-liquid interface aerosol exposure system was used to provide a more biologically relevant exposure system compared to submerged experiments, with cells exposed to either the complete aerosol (particle and gas phase), or the gas phase only (with particles filtered out). Data from cytotoxicity assays were integrated with metabolomics and proteomics analyses, including stable isotope-assisted metabolomics, in order to uncover pathways affected by combustion aerosol exposure in macrophages. Through this approach, we determined differing phenotypic effects associated with the different components of aerosol. The particle phase of diluted combustion aerosols was found to induce increased cell death in macrophages, while the gas phase was found more to affect the metabolic profile. In particular, a higher cytotoxicity of DF aerosol emission was observed in relation to the HFO aerosol. Furthermore, macrophage exposure to the gas phase of HFO leads to an induction of a pro-inflammatory metabolic and proteomic phenotype. These results validate the effects found in lung epithelial cells, confirming the role of inflammation and cellular stress in the response to combustion aerosols.
Highlights
Air pollution from anthropogenic sources are consistently associated with adverse health effects, such as asthma, cardiovascular problems, and cancer [1, 2]
Chemical and physical properties of the ship engine exposure aerosol In order to understand the composition of the aerosols that the cells were exposed to, analysis of the chemicals in both the particulate matter (PM) and the gas phase of ship engine emission from both fuels was performed
Results from this study point to a differential effect between the gas and particle phases of combustion aerosols from ship engines on RAW 264.7 macrophages. For both of the fuel types studied, the emitted particle phase has a strong impact on cytotoxicity, while the gas phase of the aerosol alone has a stronger effect on the internal metabolism of the cells
Summary
Air pollution from anthropogenic sources are consistently associated with adverse health effects, such as asthma, cardiovascular problems, and cancer [1, 2]. While useful for studying the effects of particles present in aerosols, these exposures are less representative of real-world inhalation of combustion emissions For this reason, exposure at an air-liquid interface (ALI) can be used to represent a more biologically accurate exposure to lung epithelial cells, as well as other cells present in lung tissue. Validation studies for the ALI system have been performed previously [9, 10], and there have been multiple studies that have used ALI technology to uncover novel chemical and biological insights, including more accurate modeling of particle deposition efficiencies [11], as well as the investigation of epithelial cell-macrophage co-culture responses to waste incineration emission aerosol [12]. For the reasons outlined above, ALI systems are preferred compared to submerged experiments for cell exposure, as has been discussed previously [13]
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