Re: how many sensitive cells?

[hwade@triax.com (H. Wade Patterson)]

Lester Slaback, Dave Sherer and others:

There many papers in the peer-reviewed literature that report cellular
removal and repair of radiation damage. Up to now such data has been
"overlooked" by UBIN.
Here's an example of what I mean.

Azzam, E. I.; de Toledo, S. M.; Raaphorst, G. P.; Mitchel, R. E. J.
Low-Dose Ionizing Radiation Decreases the Frequency of Neoplastic
Transformation to a Level below the Spontaneous Rate in C3H 10T1/2
Cells. Rad. Res. 146:369-373; October 1996.

Abstract:
We have previously shown that chronic exposure of plateau-phase C3H
10T1/2 cells to cobalt-60 gamma radiation at doses as low as 10 cGy
protected the cells against neoplastic transformation by a subsequent
large acute radiation exposure. We have also shown that this induced
resistance to neoplastic transformation correlated with an increased
ability to repair radiation-induced chromosome breaks. We now show that
a single exposure of quiescent cells to doses as low as 0.1 cGy also
reduces the risk of neoplastic transformation, from the spontaneous
level to a rate three- to fourfold below that level. Higher doses, up to
10 cGy at the same dose rate (0.24 cGy/min), did not reduce the
neoplastic transformation frequency further. This protective effect was
seen only in irradiated cells that were allowed to incubate at 37°C
before release from contact inhibition. Cells released into low-density
subcultures immediately after irradiation had unchanged neoplastic
transformation frequencies. These results demonstrate that low or
chronic exposure to radiation can induce processes which protect the
cell against naturally occurring as well as radiation-induced
alterations that lead to cell transformation. If similar processes are
induced in human cells, the results also suggest that a single low dose,
at background or occupational exposure levels, may in some circumstances
reduce rather than increase cancer risk, a conclusion inconsistent with
the linear no-threshold model of cancer risk from radiation.

Best wishes to all.

-- 
Wade

mailto:hwade@triax.com

H.Wade Patterson
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Lakeview OR 97630
ph 541 947-4974