Cell digestion and genotoxicity assessment in gastric mucosa

It has been claimed that the in vivo incubation of rat gastric mucosa with a test drug, followed by labelling with tritiated thymidine and selective in vitro digestion is a suitable method for evaluating genotoxic potential. However, the method rests on the assumptions that the radiolabel released on digestion has been incorporated into damaged DNA which has undergone repair (i.e. unscheduled DNA synthesis, UDS) and that the results are not confounded by the presence of dividing cells (scheduled DNA synthesis). This study examined the method by repeating the digestion procedure on rat gastric mucosa which had been labelled with bromodeoxyuridine in vivo, to mimic the 3H-TdR experiments previously reported. Results showed that the cell digest contained a mixture of cells, including parietal cells, and that there was a 6.9 +/- 0.69% (n = 43) contamination with dividing cells over a 2-hour period of labelling. This represents a 10-fold enrichment of dividing cells as compared to intact tissue. It is concluded that measurements of total radioactivity in DNA made using this digestion method cannot be related solely to UDS, but are related to a variety of unrecognized artifacts.