Direct exposure methods for testing native atmospheres
Introduction
The analysis of complex mixtures like ambient air, diesel exhaust, environmental tobacco smoke or cigarette smoke itself represents a multifactorial problem due to the complexity of the test atmosphere. In most cases, they consist of a particulate and gas phase, including hundreds of substances, short- and long-living radicals, which undergo chemical reactions after generation. It is well known that the mixture changes both qualitatively and quantitatively in a short time (Pryor, 1992, Pryor, 1997). Therefore, toxicological investigations should be carried out under conditions resembling the in vivo situation as far as possible.
The exposure of lung cells to complex atmospheres or single components like ozone is responsible for a cascade of cellular reactions, initiating the development of chronic lung disorders or even cancer. Ozone for example, an atmospheric photochemical of major concern because of its deleterious health effects upon inhalation, has been shown to result in alterations in lung function, development of bronchial hyperresponsiveness, loss of alveolar Type I cells, an influx of inflammatory neutrophils into the airways, increased epithelial and vascular permeability, a decrease in the mitogen-induced T-cell proliferation, and increased cell mortality resulting from aerolized microbial agents delivered after exposure (Coffin and Gardner, 1972; Evans, 1984; Koren et al., 1989; Orlando et al., 1989; Seltzer et al., 1986).
The responses of lung cells to toxic gases are difficult to explain. To understand the functional and pathological disorders induced in the respiratory tract requires the investigation of the direct effects of pollutants on the state and activity of lung cells. So far, three approaches have been used: (1) animal experiments, (2) ex vivo studies of cells of bronchial lavage or biopsies and (3) in vitro systems of exposure of lung cells to pollutants under controlled conditions (Rasmussen, 1984; Wallaert et al., 2000). This paper emphasizes the evolution of the in vitro approaches which offer the possibility to expose cells of the respiratory tract directly to native atmospheres.
Section snippets
Requirements
The development of in vitro methods for the exposure of lung cells has to follow some principle requirements (Rasmussen, 1984):
- 1.
Controlled generation and monitoring of the test atmosphere to study dose-dependent effects.
- 2.
The contact between the cells and the test compounds should be as close as possible to avoid interactions, for example of oxidant gases with medium components, and to realize particle deposition and, in the case of complex mixtures, direct contact of cells and gas phase
Conclusion
Taking into consideration all the presented exposure procedures, it can be concluded that, dependent on the hypothesis to be tested, a variety of experimental approaches can be realized. The most important aspect might be the susceptibility of the system, that means a sensitive biological test system and an optimal exposure device: (1) realizing an optimal contact between cells and the test atmosphere, (2) avoiding interactions of compounds of the test atmosphere with medium components and (3)
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2019, Toxicology in VitroCitation Excerpt :They are time and cost consuming, showing anatomical and physiological differences compared to the e.g. human lung, and thus, making a translation from animals to humans difficult (Faber and McCullough, 2018; Lacroix et al., 2018; Da Silva and Sørli, 2018). Therefore, significant research efforts have been invested to develop adequate non-animal inhalation toxicity testing models (e.g. in vitro cell cultures, lung-on-a-chip models, ex vivo human precision cut lung slices) or computer-based approaches that predict the biological effects based on the structure of a chemical or the deposition pattern of a substance in the respiratory tract, e.g. QSAR (quantitative structure-activity relationship) or CFD (computational fluid dynamic) models (Clippinger et al., 2018a; Huh et al., 2010; Clippinger et al., 2018b; Clippinger, 2018; Sewald and Braun, 2013; Veith et al., 2009; Aufderheide, 2005). In terms of in vitro cell culture methods, test systems can vary in complexity from submerged mono- or co-cultures to aerosol systems exposing cell cultures at the air-liquid interface (ALI) (Clippinger et al., 2018a; Thorne et al., 2018).