[ RadSafe ] Bystander Effect" Hints at Dangers of Low-Dose Radiation

Christopher Van Den Bergen Christopher.Van-Den-Bergen at adm.monash.edu.au
Wed Aug 20 01:59:43 CDT 2008

Interesting study. While the science is sound, the radiophobia (possibly) 
added by the news reporter is a problem.


ROY HERREN <royherren2005 at yahoo.com>
radsafe at radlab.nl
20/08/2008 04:49 PM
[ RadSafe ] Bystander Effect" Hints at Dangers of Low-Dose Radiation

Bystander Effect" Hints at Dangers of Low-Dose Radiation
By Jocelyn Kaiser
ScienceNOW Daily News
18 August 2008That lead apron you wear during a dental x-ray is supposed 
to protect the rest of you from radiation. But it may not work very well, 
according to a new study. When cancer-prone mice were placed in lead 
containers and irradiated on just the lower half of their bodies, they 
developed brain tumors. The results suggest that radiation could be 
riskier than scientists thought. 
The study builds on a surprising effect, first observed 16 years ago. When 
cells in culture are exposed to ionizing radiation, even those not 
directly hit sustain damage to chromosomes. Apparently, the irradiated 
cells pass on a distress signal or emit some chemical that breaks the DNA 
of neighboring cells (ScienceNOW, 7 September 2005). Although this 
"bystander effect" has been observed in tissue culture and recently in 
living animals, no experiments have yet linked it to the main reason for 
concern: Bystander effects might trigger cancer. Some scientists even 
suspect the opposite--that the bystander responses could protect against 
the disease by killing damaged cells. 
Now it seems that the cancer risk is real. Radiation oncologist Anna Saran 
at the Italian National Agency for New Technologies, Energy and the 
Environment in Rome and colleagues studied mice with a mutation in a gene 
called Patched that makes them susceptible to brain tumors early in life. 
They placed newborn mice in lead shields that protected their heads and 
upper bodies, then zapped them with high-dose x-rays, or about 12,000 
times the dose of a dental or chest x-ray. The scientists found that the 
cerebellums of these animals had higher than normal amounts of DNA damage 
and apoptosis, or programmed cell death. By 40 weeks of age, 39% of the 
shielded mice had developed brain tumors. That's a lot considering that 
the rate was 62% in Patched mice that were irradiated all over, including 
their heads. Patched mice that weren't irradiated did not develop brain 
When the team injected the shielded mice with a chemical that blocks 
cell-to-cell communication before irradiating them, they detected no DNA 
breaks and the amount of apoptosis decreased more than threefold. Even 
though the irradiated tissues are far away from the brain, they are 
connected by neurons that could be passing on bystander signals, Saran 
says. The results appear online this week in the Proceedings of the 
National Academy of Sciences. 
"This is a milestone paper," says Columbia University radiation physicist 
David Brenner. He suggests that current estimates of cancer risk from low 
doses of radiation--say, from naturally occurring radon and diagnostic 
tests--may underestimate the danger by failing to take into account 
bystander effects. To learn more, however, the mouse work should be 
repeated with lower doses of radiation, Saran says.

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