Little and Wakeford, Rad Research, Dec 2001

[muckerheide <muckerheide@attbi.com>]

Friends,



Note the following "LNT establishment" abstract. It partially recognizes

that the presumption that the bystander effect can reflect increased risk at

low doses can not be valid,  though this is short of recognizing that the

bystander effect is intrinsic to the intercellular signaling that enables

adaptive response and hormetic effects.



Regards, Jim

============



Radiat Res 2001 Dec;156(6):695-699



The Bystander Effect in C3H 10T Cells and Radon-Induced Lung Cancer.



Little MP, Wakeford R.



Department of Epidemiology and Public Health, Imperial College of Science,

Technology and Medicine, St. Mary's Campus, Norfolk Place, London W2 1PG,

United Kingdom; Author to whom correspondence should be addressed at

Department of Epidemiology and Public Health, Imperial College of Science,

Technology and Medicine, St. Mary's Campus, Norfolk Place, London W2 1PG,

UK: e-mail mark.little@ic.ac.uk.



Bystander effects, whereby cells that are not directly exposed to radiation

exhibit adverse biological effects, have been observed in a number of

experimental systems, including C3H 10T(1/2) cells exposed to alpha-particle

radiation. The bystander effect implies that risks from exposure to low

doses of radiation obtained by linear extrapolation from data for high-dose

exposures might be substantial underestimates. The best estimate of the

ratio of the lung cancer risk among persons exposed to low (residential)

doses of radon daughters to that among persons (underground miners) exposed

to high doses of radon daughters is in the range of 2.4-4.0, with an upper

95% confidence limit of about 14. Assuming that the bystander effect

observed in the in vitro C3H 10T(1/2) cell system applies to human lung

cells in vivo, these epidemiological data imply that the central estimate of

the number of neighboring cells that can contribute to the bystander effect

is between 0 and 1, with an upper 95% confidence limit of about 7. As a

consequence, the bystander effect observed in the experimental C3H 10T(1/2)

cell system probably does not play a large part in the process of

radon-induced lung carcinogenesis in humans.



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