Why effects of LDR differ from metabolism

["Ted Rockwell" <tedrock@CPCUG.ORG>]

Friends:



Several people asked, if DNA mutations from LDR are so few compared with

those caused by metabolism, why does the body respond (beneficially) to LDR?

How is the LDR signal seen in such a much larger metabolic background?



Good question.  The answer has two parts.  First, when LDR is applied

therapeutically in a hospital, the dose is delivered in 1-minute shots, two

or three a week for five weeks.  This is a very high dose RATE during the

one minute irradiation, so it clearly gets the body's attention.



But that doesn't apply to the chronic doses received by radiation workers,

downwinders, and people living in high natural radiation areas.  In those

cases, the difference results from the fact that the metabolic effect

diffuses throughout the body in a steady flow, like the light of the full

moon.  But radiation affects the body more locally in space and time, like

flashes of summer lightning.  Dr. Sukosky explained it well in his earlier

post (excerpted below).  For a given cell that is, or is not, struck by

radiation, the effect is very attention-getting, even though comparatively

fewer cells are affected.



There are intercellular reactions which play a part, but ultimately a cancer

initiates (or not) in individual cells.



Dr. Sukosky's post follows:



What's so special is there are spatial and temporal differences

between DNA mutations produced by ionizing radiation compared to

DNA mutations produced by metabolism. Radiation occurs in focal

bursts while metabolism is random, relatively uniform and

continuously produced.  Because of these spatial and temporal

differences, different reactive oxygen species are produced by

ionizing radiation compared to metabolism. When radiation produced

reactive oxygen species interact with DNA, the result is significantly

different types of DNA mutations compared to mutations from metabolism

produced reactive oxygen species.



Numerous studies (some of which are cited below) have demonstrated

that low-dose radiation increases DNA damage-control biosystem activity

which decreases metabolic mutations and results in lower cancer

mortality and increased life-span. The increased DNA damage-control

biosystem activity is associated with increased prevention, removal

and repair of DNA damage.



If you're interested in the detailed description and experimental

testing of the hypothesis, Dr. Pollycove presents it very clearly in

an excellent paper which is cited in the first reference below.





REFERENCES



Pollycove, M.  Dose Response of the Organism to Ionizing Radiation.

SNM REIR Continuing Education:  Radiobiology II.  SNM Annual Meeting,

Saint Louis, June 4, 2000.



Feinendegen LE, Loken MK, Booz J, Muhlensiepen H, Sondhaus CA, Bond VP.

Cellular mechanisms of protection and repair induced by radiation

exposure and their consequences for cell system responses.  Stem Cells

13 (Suppl. 1): 7-20.



Feinendegen LE, Sondhaus CA, Booz J, Bond VP, Muhlensiepen H.

Radiation effects induced by low doses in complex tissue and their

relation to cellular adaptive responses.  Mutation Res. 358:199-205

(1996).



Yamaoka K. Increased SOD activities and decreased lipid peroxide in

rat organs induced by low X-irradiation.  Free Radical Biol Med 11:3-7

(1991).



Le XC, Xing JZ, See J, Leadon SA.  Weinfeld M.  Inducible repair of

thymine glycol detected by and ultra sensitive assay for DNA damage.

Science 280:1066-1069 (1998).



Anderson RE.  Effects of low-dose radiation on the immune response.

Chapt 5 In:  Biological Effects of Low Level Exposures to Chemicals

and Radiation (Calabrese EJ, ed). Chelsea, MI: Lewis Publishers; 1992:

95-112.



Makinodan T, James SJ.  T cell potentiation by low dose ionizing

radiation: possible mechanisms.  Health Phys 59(1):29-34 (1990).



Duke RD, Ojcius DM, Young JD-E.  Cell suicide in health and disease.

Scientific American Dec:80-87 (1996).





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