Measurement of DNA base damage in cells exposed to low doses of gamma-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 wit h 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 anal ysis was performed to measure 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGu o) levels in cells. Results: A correlation between these assays allowed the determination of th e 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 f ound. For the strand breaks and alkali-labile sites, the background level w as 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 e stimate DNA base damage in cells exposed to low doses of gamma-radiation.