Influence of in vitro low-level gamma-radiation on the UV-induced DNA repair capacity of human lymphocytes - analysed by unscheduled DNA synthesis (UDS) and comet assay

Unscheduled DNA synthesis (UDS) induced by ultraviolet radiation (UV) was s tudied in human lymphocytes after exposing blood samples in vitro to doses ranging between 1 and 10 mGy gamma-radiation, by way of measuring tritiated thymidine (H-3-TdR) uptake in the DNA of these lymphocytes. The results in dicate that samples pre-exposed to gamma-ray doses ranging between 2.5 and 4 mGy show higher UDS levels compared with those preexposed to doses of les s than 2.5 or more than 4 mGy. These results were verified by studying the rate of removal of UV-induced photoproducts using the comet assay. The reas on for the increase in DNA repair capacity in this dose range is discussed in comparison with earlier reports on this phenomenon. The DNA repair capac ity with respect to inter-individual variability and age is also analysed. The study implies that the comet assay is a simple and sensitive visual met hod to track nucleotide excision repair and hence can be used to estimate U V-induced DNA repair in the place of the more reliable yet cumbersome and t ime-consuming, grain-counting autoradiographic technique.