Measurement of DNA base damage in cells exposed to low doses of γ-radiation:: comparison between the HPLC-EC and comet assays

Purpose: Two different methods aimed at measuring DNA damage were compared. Monocytes were exposed to Co-60 gamma-rays and the level of DNA damage was determined using either the HPLC-EC or comet assay. Materials and methods: The alkaline comet assay was used in association with the Fpg and Endo III DNA glycosylases to estimate the amount of modified bases together with strand breaks and alkali-labile sires. The HPLC-EC analysis was performed to measure 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) levels in cells. Results: A correlation between these assays allowed the determination of the steady-slate level and the yield of Fpg sensitive sites (assimilated to 8-oxodGuo), which were estimated to be 0.18 per 10(6) bp and 0.044 per 10(6) bp per Gy, respectively. Similar levels of Endo III sensitive sites were found. For the strand breaks and alkali-labile sites, the background level was 0.26 per 10(6) bp and the yield 0.123 per 10(6) bp per Gy. Discussion: The modified comet assay appears to be an appropriate tool to estimate DNA base damage in cells exposed to low doses of gamma-radiation.