AW: [ RadSafe ] Danger of ADJACENT HIGH-Dose Radiation

Thu Aug 21 03:41:27 CDT 2008

Grant,

the mechanisms responsible for - the nowadays somewhat indiscriminately so called - bystander effects are manifold. They comprise both genuine short-range cell to cell communication via specific communication channels as well as less specific wide range signal transfer via universal 'second messengers', e.g., of the humoral system. 

Personally I reserve the more recent term bystander effect to those instances where cells which have received (very) low radiation doses signal their resulting response to cells of the same organ or tissue which have not received any radiation at all. The - usually few - cells 'hit' do transmit their signals via cell and tissue specific communication channels whose ordinary function (conceivably) is to ensure tissue homeostasis/control. 

For such instances as described by Mancuso et al. (2008) where the signals arise from cells rather heavily(!) exposed and where they affect cells in distant organs, I prefer the term abscopal effects - effects which have been described since decades before the genuine bystander effect. Although much of the communication system involved is yet to be elucidated the general endocrine system almost certainly is a mayor player. 

Contrary to the quoted statement by Brenner, these results have no import whatsoever on radiation protection at low doses. See also the corresponding remark from K S Parthasarathy, Mi 20.08.2008 11:56

Regards, Rainer

Dr. Rainer Facius
German Aerospace Center
Institute of Aerospace Medicine
Linder Hoehe
51147 Koeln
GERMANY
Voice: +49 2203 601 3147 or 3150
FAX:   +49 2203 61970

________________________________

Von: radsafe-bounces at radlab.nl im Auftrag von NIXON, Grant
Gesendet: Mi 20.08.2008 22:09
An: HOWARD.LONG at comcast.net; ROY HERREN; radsafe at radlab.nl
Betreff: RE: [ RadSafe ] Danger of ADJACENT HIGH-Dose Radiation 

To add to Howard's comment:

Perhaps the mechanism for the DNA damage to adjoining tissue (the
so-called "bystander effect") is nothing more than a propagated
free-radical reaction having nothing to do with cell-to-cell
communication. The high doses would liberate such large numbers of
free-radicals that the affected perimeter of affected tissues would
increase on physical grounds alone (diffusion theory coupled with target
theory). The "chemical that blocks cell-to-cell communication" may
simply be a free-radical scavenger.

Grant I. Nixon, Ph.D., P.Phys.
Science Specialist (Dosimetry/Physics/Engineering)
BEST Theratronics
413 March Road
Ottawa, ON  K2K 0E9
Canada
tel. (613) 591-2100 x2869
fax. (613) 591-2250

-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On
Behalf Of HOWARD.LONG at comcast.net
Sent: Wednesday, August 20, 2008 12:36 PM
To: ROY HERREN; radsafe at radlab.nl
Subject: [ RadSafe ] Danger of ADJACENT HIGH-Dose Radiation

So, "high dose radiation - 12,000 times - chest x-ray" affects adjacent
tissue?
Would other severe injury, like crushed arm, affect the rest of the
body? Of course!

Why the surprise?

Why the false headline that it  "Hints at Dangers of Low Dose
Radiation"?

Hormesis, low dose good where high dose bad, must be taught. 
We must correct this disinformation by fearmongers
to dismantle over-regulation and liberate nuclear power.

Howard Long

-------------- Original message --------------
From: ROY HERREN <royherren2005 at yahoo.com>

> http://sciencenow.sciencemag.org/cgi/content/full/2008/818/3
>
> 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 cancer.
> 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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