Effect of low doses and low dose-rates of gamma radiation on DNA damage in human peripheral blood leukocytes using comet assay

Comet assay is a sensitive technique and it provides a unique opportunity to investigate intercellular differences in DNA damage and repair in any eukaryotic cell population. This assay can be used to detect DNA single strand breaks, alkali-labile sites and incomplete DNA repair sites, under alkaline conditions and DNA double strand breaks under neutral condition. We report here our observations on the low-dose (1.25, 2.50, 5.0 and 10.0 cGy) effects of gamma rays on DNA damage in human peripheral blood leukocytes. In a separate experiment on dose-rate, human blood samples were exposed to a total dose of 10.0 cGy at different dose-rates (0.46, 0.93 and 1.85 cGy/ min) of gamma rays using an industrial radiographic camera. Cells were processed by alkaline comet assay, stained in SYBR Green II and analysed using an imaging software SCGE-Pro, developed in our laboratory for quantification of DNA strand breaks using comet assay. Various comet parameters, e.g., tail length, % DNA in tail and tail moment, were measured for each comet. Analysis of data revealed significant increase in DNA damage even at the lowest dose of 1.25 cGy. Lower dose-rate produced higher DNA damage as compared to the higher dose-rate.