Journal
BRITISH JOURNAL OF CANCER
Volume 96, Issue 11, Pages 1707-1710Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/sj.bjc.6603775
Keywords
low dose; low dose rate; senescence; DNA double strand break; high LET radiation
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To investigate the long-term biological effect of extreme low dose ionising radiation, we irradiated normal human fibroblasts (HFLIII) with carbon ions (290 MeVu(-1), 70 keV mu m(-1)) and gamma-rays at 1 mGy (total dose) once at a low dose rate (1 mGy 6 - 8 h(-1)), and observed the cell growth kinetics up to 5 months by continuous culturing. The growth of carbon-irradiated cells started to slow down considerably sooner than that of non-irradiated cells before reaching senescence. In contrast, cells irradiated with gamma-rays under similar conditions did not show significant deviation from the non-irradiated cells. A DNA double strand break (DSB) marker, gamma-H2AX foci, and a DSB repair marker, phosphorylated DNA-PKcs foci, increased in number when non-irradiated cells reached several passages before senescence. A single low dose/low dose rate carbon ion exposure further raised the numbers of these markers. Furthermore, the numbers of foci for these two markers were significantly reduced after the cells became fully senescent. Our results indicate that high linear energy transfer (LET) radiation (carbon ions) causes different effects than low LET radiation (gamma-rays) even at very low doses and that a single low dose of heavy ion irradiation can affect the stability of the genome many generations after irradiation.
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