Lack of evidence for low-LET radiation induced bystander response in normal human fibroblasts and colon carcinoma cells.
OBJECTIVE
To investigate radiation-induced bystander responses and to determine the role of gap junction intercellular communication and the radiation environment in propagating this response.


METHODS
We used medium transfer and targeted irradiation to examine radiation-induced bystander effects in primary human fibroblast (AG01522) and human colon carcinoma (RKO36) cells. We examined the effect of variables such as gap junction intercellular communication, linear energy transfer (LET), and the role of the radiation environment in non-targeted responses. Endpoints included clonogenic survival, micronucleus formation and foci formation at histone 2AX over doses ranging from 10-100 cGy.


RESULTS
The results showed no evidence of a low-LET radiation-induced bystander response for the endpoints of clonogenic survival and induction of DNA damage. Nor did we see evidence of a high-LET, Fe ion radiation (1 GeV/n) induced bystander effect. However, direct comparison for 3.2 MeV alpha-particle exposures showed a statistically significant medium transfer bystander effect for this high-LET radiation.


CONCLUSIONS
From our results, it is evident that there are many confounding factors influencing bystander responses as reported in the literature. Our observations reflect the inherent variability in biological systems and the difficulties in extrapolating from in vitro models to radiation risks in humans.
Sowa
Marianne B
MB
Molecular and Cellular Biology, Pacific Northwest National Laboratory, Richland, Washington 99354, USA. Marianne.sowa@pnl.gov
Goetz
Wilfried
W
Baulch
Janet E
JE
Pyles
Dinah N
DN
Dziegielewski
Jaroslaw
J
Yovino
Susannah
S
Snyder
Andrew R
AR
de Toledo
Sonia M
SM
Azzam
Edouard I
EI
Morgan
William F
WF
D024201:Bystander Effect / Q000502:physiology / Q000528:radiation effects*; D002460:Cell Line; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy; D003114:Colony-Forming Units Assay; D004249:DNA Damage; D004307:Dose-Response Relationship, Radiation; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects; D017629:Gap Junctions / Q000528:radiation effects; D006657:Histones / Q000378:metabolism; D006801:Humans; D018499:Linear Energy Transfer; D015162:Micronucleus Tests; D014410:Tumor Stem Cell Assay
C468783:H2AX protein, human; D006657:Histones