DNA damage induced in cells by γ and UVA radiation as measured by HPLC/GC-MS and HPLC-EC and comet assay

The aim of the work was to measure DNA damage induced within tumoral human monocytes by gamma rays, UVA radiation, and exogenous photosensitizers. The accurate HPLC-EC assay was used to determine the level of 8-oxodGuo. The formation of FapyGua and FapyAde was monitored by HPLC/GC-MS analyses after formic acid hydrolysis at room temperature. For this purpose, cells were exposed to relatively high doses of gamma rays and WA radiation. The extent; of formation of FapyGua in the DNA of cells exposed to gamma rays was estimated to be more than 2-fold higher than that of 8-oxodGuo, i.e,, about 0.027 lesion per 10(6) bases per Gy. The yield of FapyAde was estimated to be 1 order of magnitude lower. The latter results were used to calibrate the alkaline comet assay associated with DNA N-glycosylases. The latter approach allowed the determination of the background level (0.11-0.16 Fpg-sensitive site/10(6) bases) and the yields of strand breaks and DNA base damage upon low irradiation doses. Insights into the mechanism of radiation-induced DNA damage were gained from these measurements. A major involvement of O-1(2) with respect to hydroxyl radicals and type I photosensitization was thus observed within cells exposed to UVA radiation.