RE: LNT clarification

[John_Sukosky@DOM.COM]

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).









<SNIP>

Thus damage by radiation occurs the same way as from metabolism.  But for

each mutation caused by radiation, several million are caused by metabolism.

Thus the effort to reduce the number of radiation impacts is

inconsequential.

<SNIP>



........which I still find very puzzling -- if radiation damage is "the

same," then what's so special about it, that a relatively insignificant

amount (ie. relative to damage caused by metabolism ) can stimulate an

immune response -- hormesis -- while the metabolism does not ?



I know I asked this question before, but I still haven't seen a good answer

-- the laboratory data looks convincing, but surely there must be some

hypothesis attempting to explain how this could happen ? Seems to me that as

long as there isn't a reasonable hypothesis (which can be tested in some

sort of molecular biology experiments), then critics can continue to claim

that the observed LDI hormesis effects are really the result of some

confounding factor in the experiment (???).



Thanks



Jaro











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