Chemically induced DNA damage in isolated rabbit lung cells

By use of an isolation procedure including centrifugal elutriation and density gradient centrifugation, relatively pure fractions of Clara cells and type II cells were obtained from rabbit lungs. These cells and alveolar macrophages isolated by lavage were exposed to methyl methanesulfonate (MMS), 1,2-dibromo-3-chloropropane (DBCP), 1-nitropyrene (1-NP), 2-nitrofluorene (2-NF), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), N'-nitrosonornicotine (NNN), N-nitrosoheptamethyleneimine (NHMI) or phorbol 12-myristate 13-acetate (TPA). DNA damage measured as alkali-labile sites and/or single-strand breaks was then determined in the different lung cells by an automated alkaline elution system. The direct-acting compound MMS showed similar DNA-damaging effect in Clara cells, type II cells and alveolar macrophages. The nematocide DBCP, activated by both P450- and glutathione S-transferase(s)-dependent pathways, caused considerably less DNA damage in macrophages than in Clara or type II cells. Similar differences between the lung cells in induction of DNA damage as observed with DBCP were demonstrated after exposure to the activation-dependent nitrosamines NNK and NHMI and the tumor promoter TPA. The other test substances (1-NP, 2-NF, NNN) did not cause any marked DNA damage measured by the alkaline elution technique. These findings are in agreement with the known metabolic capacity of these cell types, indicating that Clara and type II cells are possible primary targets for lung toxic/carcinogenic compounds.