Dose--response of initial G2-chromatid breaks induced in normal human fibroblasts by heavy ions.
OBJECTIVE
To investigate initial chromatid breaks in prematurely condensed G2 chromosomes following exposure to heavy ions of different LET.


METHODS
Exponentially growing human fibroblast cells AG1522 were irradiated with gamma-rays, energetic carbon (13 keV/ microm, 80 keV/microm), silicon (55 keV/microm) and iron (140 keV/microm, 185keV/microm, 440keV/microm) ions. Chromosomes were prematurely condensed using calyculin-A. Initial chromatid-type and isochromatid breaks in G2 cells were scored.


RESULTS
The dose response curves for total chromatid breaks were linear regardless of radiation type. The relative biological effectiveness (RBE) showed a LET-dependent increase, peaking around 2.7 at 55-80keV/microm and decreasing at higher LET. The dose response curves for isochromatid-type breaks were linear for high-LET radiations, but linear-quadratic for gamma-rays and 13 keV/microm carbon ions. The RBE for the induction of isochromatid breaks obtained from linear components increased rapidly between 13keV/microm (about 7) and 80keV/microm carbon (about 71), and decreased gradually until 440 keV/microm iron ions (about 66).


CONCLUSIONS
High-LET radiations are more effective at inducing isochromatid breaks, while low-LET radiations are more effective at inducing chromatid-type breaks. The densely ionizing track structures of heavy ions and the proximity of sister chromatids in G2 cells result in an increase in isochromatid breaks.
Kawata
T
T
NASA Lyndon B. Johnson Space Center, Radiation Biophysics Laboratory, Houston, Texas 77058, USA. tkawata@ems.jsc.nasa.gov
Durante
M
M
Furusawa
Y
Y
George
K
K
Takai
N
N
Wu
H
H
Cucinotta
F A
FA
D001399:Azure Stains; D002244:Carbon / Q000378:metabolism; D002478:Cells, Cultured; D002842:Chromatids / Q000528:radiation effects*; D004249:DNA Damage; D004307:Dose-Response Relationship, Radiation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000528:radiation effects*; D016195:G2 Phase / Q000528:radiation effects*; D005720:Gamma Rays; D006801:Humans; D007477:Ions; D007501:Iron / Q000378:metabolism; D008387:Marine Toxins; D010080:Oxazoles / Q000494:pharmacology; D012825:Silicon / Q000378:metabolism
D001399:Azure Stains; D004791:Enzyme Inhibitors; D007477:Ions; D008387:Marine Toxins; D010080:Oxazoles; D002244:Carbon; C059041:calyculin A; D007501:Iron; D012825:Silicon