Photochemical Products in Urban Mixtures Enhance Inflammatory Responses in Lung Cells

Abstract

Complex urban air mixtures that realistically mimic urban smog can be generated for investigating adverse health effects. "Smog chambers" have been used for over 30 yr to conduct experiments for developing and testing photochemical models that predict ambient ozone (O(3)) concentrations and aerosol chemistry. These chambers were used to generate photochemical and nonirradiated systems, which were interfaced with an in vitro exposure system to compare the inflammatory effects of complex air pollutant mixtures with and without sunlight-driven chemistry. These are preliminary experiments in a new project to study the health effects of particulate matter and associated gaseous copollutants. Briefly, two matched outdoor chambers capable of using real sunlight were utilized to generate two test atmospheres for simultaneous exposures to cultured lung cells. One chamber was used to produce a photochemically active system, which ran from sunrise to sunset, producing O(3) and the associated secondary products. A few hours after sunset, NO was added to titrate and remove completely the O(3), forming NO(2). In the second chamber, an equal amount of NO(2) and the same amount of the 55-component hydrocarbon mixture used to setup the photochemical system in the first side were injected. A549 cells, from an alveolar type II-like cell line grown on membranous support, were exposed to the photochemical mixture or the "original" NO(2)/hydrocarbon mixture for 5 h and analyzed for inflammatory response (IL-8 mRNA levels) 4 h postexposure. In addition, a variation of this experiment was conducted to compare the photochemical system producing O(3) and NO(2), with a simple mixture of only the O(3) and NO(2). Our data suggest that the photochemically altered mixtures that produced secondary products induced about two- to threefold more IL-8 mRNA than the mixture of NO(2) and hydrocarbons or O(3). These results indicate that secondary products generated through the photochemical reactions of NO(x) and hydrocarbons may significantly contribute to the inflammatory responses induced by exposure to urban smog. From previous experience with relevant experiments, we know that many of these gaseous organic products would contribute to the formation of significant secondary organic particle mass in the presence of seed particles (including road dust or combustion products). In the absence of such particles, these gaseous products remained mostly as gases. These experiments show that photochemically produced gaseous products do influence the toxic responses of the cells in the absence of particles.

Early history and rationale for outdoor chamber work at the University of North Carolina

“…The results were very interesting in that the toxicological endpoints from the irradiated smog mixture were significantly larger than either the ozone-only or precursor-only exposure results. [66] This was an early example of the effect of atmospheric chemistry on the toxicity of air pollutant mixtures. It showed the enhanced toxicity effect, above that from ozone and initial primary reactants, due to the presence of secondary toxic compounds that were produced in the atmosphere.…”

Air Pollution and Adverse Pregnancy Outcome

“…It may be that exposure of the fetal lung to high concentrations of pro-inflammatory cytokines is the cause of this increased susceptibility (Miralles et al, 2002). Photochemically produced gaseous products influence the toxic responses of cells, such as the production of cytokine, in the absence of particles (Sexton et al, 2004). PM 10 is responsible for the production and release of inflammatory cytokines by the respiratory tract epithelium, as well as for activation of the transcription factor NfkappaB (Baeza-Sqiban et al, 1999;Bonvallot et al, 2001).…”

Gaseous VOCs rapidly modify particulate matter and its biological effects – Part 2: Complex urban VOCs and model PM

“…The A549 cells were cultured and prepared for exposure as explained previously (Jaspers et al, 1997;Doyle et al, 2004;Sexton et al, 2004;de Bruijne et al, 2009;Ebersviller et al, 2012a). The Gas In Vitro Exposure System (GIVES) and Electrostatic Aerosol in Vitro Exposure System (EAVES) have also been described in detail previously (Ebersviller et al, 2012a;Lichtveld et al, 2012;de Bruijne et al, 2009;Doyle et al, 2004Doyle et al, , 2007Sexton et al, 2004). Briefly, these systems allow the cellular toxicity of the gaseous and particle phase components of the same air pollution mixture to be evaluated independently of one another, and with no substantive modification to the sample prior to exposure.…”

“…A549 human respiratory cells are a commercially available cell line that have been shown to react in a manner that is representative of the human airway in vivo (Lieber et al, 1976;ATCC, 2011). The A549 cells were cultured and prepared for exposure as explained previously (Jaspers et al, 1997;Doyle et al, 2004;Sexton et al, 2004;de Bruijne et al, 2009;Ebersviller et al, 2012a). The Gas In Vitro Exposure System (GIVES) and Electrostatic Aerosol in Vitro Exposure System (EAVES) have also been described in detail previously (Ebersviller et al, 2012a;Lichtveld et al, 2012;de Bruijne et al, 2009;Doyle et al, 2004Doyle et al, , 2007Sexton et al, 2004).…”

“…The effects of photochemical-ageing and gas and particle interactions have recently begun to be evaluated for their impact on the relative risk associated with exposure Sexton et al, 2004;Doyle et al, 2007;Lichtveld et al, 2012). Previous experiments using outdoor irradiation chambers have measured significant changes in chemical composition as air pollution mixtures age in sunlight and, in most cases, have measured an accompanying increase in toxicity.…”