An in vitro lung epithelial cell system for evaluating the potential toxicity of inhalable materials

Assays have been developed using a lung epithelial cell strain, LEC, for evaluating the cytotoxicity and genotoxicity of gases, vapours, particles and fibres. LEC was derived from an adult male Fischer 344 rat and was cultured continuously in vitro for over 60 passages. The cells had an epithelial morphology, a near-diploid modal chromosome number of 43-44, and properties of untransformed cells. Lamellar inclusion bodies were found in the cytoplasm, suggesting that LEC originated from the type II alveolar cells. The ability to LEC to metabolize xenobiotics was demonstrated by the formation of polar metabolites from benzo[a]pyrene, the induction of gene mutation by promutagens in a metabolically incompetent cell line (Chinese hamster ovary cells) after co-cultivation with LEC, and the induction of sister chromatid exchange in LEC by promutagens. LEC will grow on collagen gel in the absence of an overlying medium, thereby constituting an in vitro exposure system closely resembling lung epithelium in vivo. The cytotoxic potential of inhalable agents, including nitrogen dioxide, phenol vapours, formaldehyde, automobile exhaust, titanium dioxide and chrysotile and crocidolite forms of asbestos was studied. The in vitro cytotoxicity appeared to correlate well with the known in vivo pulmonary toxicity of the substances studied. Using chromosomal-aberration induction as an endpoint, chrysotile asbestos was found to be genotoxic to LEC. Our results suggest that LEC may be a useful in vitro system for the evaluation of the toxic potential of inhalable materials.