Re: Laymans questions on hormesis and LNT

["Cary Renquist" <crenquis@med.umich.edu>]

Jim, ;-)



DSBs in and of themselves are not necessarily detrimental....

Essentially the hypothesis is that _improperly_repaired_DSBs_ 

are detrimental e.g. cancer -- unrepaired DSBs are fatal to the 

cell (whether or not cell kill is detrimental depends on how many

cells are involved).

The study seemed to show that for low dose rates (I forget the

absolute number) cells do not repair DSBs, rather the cells usually

go on to die -- no big problem if a few cells die.  If this is true in situ,

then there should be less risk of cancer induction for low doses.



Cary







>>> John Jacobus <crispy_bird@yahoo.com> 08/29/2003 15:01:53 >>>

Carl,

I think that this is part of the problem.  We are able

to determine DS breaks and observe their repair or

non-repair.  The arguement is the DS breaks are

precursors to cancer or other effects.  I doubt that

in all cases this is true, whether or not repair takes

place.  However, if you say that DS breaks are

detrimental, then we need to control does down to

those levels.



Note that hormesis does not even have to be invoked in

this arguement.  Yet, it allows more flexibility in

establishing risk limits.



--- Cary Renquist <crenquis@med.umich.edu> wrote:

> 

> It seems that experimental techniques are getting

> down to the level 

> where DSB's and repair processes can be examined

> quite closely:

> Mentioned earlier in the year: 

>    Rothkamm, K. and M. Löbrich. 2003. Evidence for a

> lack of DNA double-strand break 

>    repair in human cells exposed to very low X-ray

> doses. Proc. Natl. Acad. Sci. USA, 

> 

> One speculation based on their research is: at low

> dose rates cells do not attempt to repair DSBs --

> thus

> eliminating the chance of an improper repair.  Not

> exactly hormesis, but if that hypothesis stands up

> under

> further research it lends credence a dose-response

> model at variance to the LNT.

> . . .



=====

-- John

John Jacobus, MS

Certified Health Physicist

e-mail:  crispy_bird@yahoo.com 



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