Broken DNA. fluorescent blobs (green) show the double-stranded DNA breaks in irradiated cells (blue).
ionizing radiation can break both strands of the DNA double helix - a possible cause of cancer if not secured properly. The number of breaks increases with higher doses of radiation, but new research found that cells exposed to low doses can have a more difficult time to repair the damage that blasted cells with high doses. However, researchers say there is no reason to cancel your next appointment x-ray.
Until recently, researchers had no way to study DNA damage and repair following exposure to low doses of radiation. Instead, the effects had to be extrapolated from examining workers exposed to high radiation in nuclear facilities and the survivors of the Japanese atomic bomb. In the new study, biophysicists and Kai Markus Löbrich Rothkamm at the University of Saarland in Homburg, Germany, took advantage of a new method that uses fluorescent markers to highlight double-strand breaks.
The pair zapped human fibroblast cells with radiation ranging from 1.2 to 20 milligray (standard radiographs provide between 1 and 10 milligray). Higher doses caused more damage than lower doses. Löbrich and Rothkamm could look under repair breaks, indicated by blinking of the eye markers. To their surprise, the quality of damage control varies. No breaks were repaired for 4 days after exposure to 1.2 milligray. Cells exposed to higher doses regularly repaired breaks, but stopped once about a break with 10 cells remained - the same level as in cells exposed to 1.2 milligray, reports online this week in team the Proceedings of the national Academy of Sciences . Cells with damaged DNA are killed when scientists stimulated their growth and division.
The discovery suggests that the DNA repair system works only until the number of breaks is similar cells by 10. There is no ready explanation for this cutoff point, Löbrich said, but as long as the damage does not affect too many cells "it makes perfect sense for an organization not to fix any double-strand breaks." Because repairs are often imperfect, it may be safer to simply kill cells, he said.
"It is a very provocative idea," said William Bonner, a molecular biologist at the National Cancer Institute in Bethesda, Maryland. Monitoring of double-strand breaks should allow researchers to "really start getting accurate data on the effects of low-dose radiation. " But the results do not mean that low doses of radiation are particularly unhealthy, says biophysicist Richard Setlow of Brookhaven National Laboratory in Upton, New York. "There is very little damage and it will not have a big effect."
Related Sites
The site of Markus Löbrich
The site of William Bonner
Site of Richard Setlow
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