Detection and comparison of In vivo DNA strand breaks in the respiratory tract of rats after exposure to gamma irradiation or radon and progeny inhalation

Recently developed techniques based on end-labelling of DNA strand breaks may help to identify DNA damages. Two of them 'in situ end-labelling' (ISEL) and 'dUTP nick end labelling' (TUEL) have been used in combination with confocal microscopy and co-localization techniques in order to verify if DNA fragmentation are distinguishable among all the target epithelial cells of the respiratory tract of the rats. Such approach is of great interest in in vivo studies of alpha-induced DNA damages after exposure of rats to different levels of radon progeny. It has been shown in previous experiments that the increase of lung cancers in rats is dose rate-dependent with a tapering off for dose-rate at very low doses. Our preliminary results suggested that ISEL and TUNEL techniques are able to detect low levels of DNA damages induced after irradiation but that both of them are very sensitive to fixation and pretreatment conditions. This imply the necessity to routinely apply a number of well standardized criteria for a specific evaluation of the labelling. The high cellular resolution of confocal microscopy allows to compare the spatial distribution and the accumulation or repair of DNA damages either in individual cells or among the target tissue. Moreover, experiments are still in progress to identify and quantify the number and the intensity of epithelial stained cells. (authors)