Experimental in vitro exposure methods for studying the effects of inhalable compounds

Abstract

Analysis of the cellular reactions to complex mixtures such as ambient air, diesel exhaust, or cigarette smoke in vitro is a comprehensive approach because of the complexity of the test atmosphere. Smoke, in particular, represents a mixture of thousands of substances, including short- and long-living radicals in both the gaseous and particulate phases of the aerosol (Hoffmann and Wynder 1986). These compounds undergo chemical reactions that will change the mixture qualitatively and quantitatively in a short time after smoke generation (Pryor 1992, 1997). Thus, all toxicological investigations should be carried out under conditions that are as relevant as possible to the in vivo smoking situation. The exposure of lung cells to such complex atmospheres will be responsible for either cell injury or cell activation associated with the overexpression of mRNA or the release of various mediators. Therefore, attention should be given to cellular reactions induced by cigarette smoke as a possible cause for the development of chronic lung disorders. Characterization of the early cellular and molecular events plays an important role in understanding the mechanisms involved in chronic lung diseases. Bronchial epithelial cells, alveolar macrophages, and alveolar epithelial cells are in close and permanent contact with inhalable compounds. They participate, at least in part, for example, in the development of inflammatory reactions, commonly described after exposure to air pollutants. The understanding of the functional and pathological disorders resulting from the inhalation of toxic gases and of complex mixtures like cigarette smoke in the respiratory tract requires investigations of the direct effect of such compounds concerning the state and activity of the cells. Here, in vitro systems offer (1) a variety of human cells including bronchial and alveolar cells as well as macrophages for use in monolayer or coculture systems; (2) the analysis of individual cell type responses to complex mixtures or fractions, allowing a better understanding of the independent contribution of this cell type to a particular response; and (3) in vitro exposure conditions that in general can be controlled and reproduced more easily (Leikauf and Driscoll 1993; Wallaert et al. 1996, 2000). © Springer-Verlag Berlin Heidelberg 2006.