[Unscheduled DNA synthesis (UDS) induced by N-methyl-N'nitro-N-nitrosoguanidine (MNNG) in human gastric mucosal cells].

DNA repair synthesis as estimated by the unscheduled incorporation of tritiated thymidine (3H-TdR) is a useful, economical, and rapidly performed bioassay for detecting DNA-damaging agents. The purpose of this study was to establish the method of MNNG induction and measurement of UDS in human gastric mucosal cells for further study of gastric carcinogenesis and its prevention. Normal gastric mucosal cells isolated from surgical specimens were exposed to various concentrations of MNNG in the presence of 5mM hydroxyurea and 10uCi/ml 3H-TdR in 1% FBS DMEM-F12 medium for 4 hours at 37 degrees C. Immediately following exposure to MNNG the capacity of gastric mucosal cells to undergo DNA synthesis was assayed by autoradiography. The results of the present study indicated that the gastric epithelial cells are capable of repairing MNNG-induced DNA damage. The UDS positive cells were revealed by increased 3H-TdR incorporation into each nucleus, and the UDS level was MNNG dose-dependent.