DNA fragmentation induced in human fibroblasts by accelerated (56)fe ions of differing energies.
DNA fragmentation was studied in the fragment size range 0.023-5.7 Mbp after irradiation of human fibroblasts with iron-ion beams of four different energies, i.e., 200 MeV/nucleon, 500 MeV/nucleon, 1 GeV/nucleon and 5 GeV/nucleon, with gamma rays used as the reference radiation. The double-strand break (DSB) yield (and thus the RBE for DNA DSB induction) of the four iron-ion beams, which have LETs ranging from 135 to 442 keV/mum, does not vary greatly as a function of LET. As a consequence, the variation of the cross section for DSB induction mainly reflects the variation in LET. However, when the fragmentation spectra were analyzed with a simple theoretical tool that we recently introduced, the results showed that spatially correlated DSBs, which are absent after gamma irradiation, increased markedly with LET for the iron-ion beams. This occurred because iron ions produce DNA fragments smaller than 0.75 Mbp with a higher probability than gamma rays (a probability that increases with LET). These sizes include those expected from fragmentation of the chromatin loops with Mbp dimensions. This result does not exclude a correlation at distances smaller than the lower size analyzed here, i.e. 23 kbp. Moreover, the DSB correlation is dependent on dose, decreasing when dose increases; this can be explained with the argument that at increasing dose there is an increasing fraction of fragments produced by DSBs caused by separate, uncorrelated tracks.
Belli
Mauro
M
Health and Technology Department, Istituto Superiore di Sanità, and INFN Sezione di Roma1, Gruppo Collegato Sanità, Roma, Italy.
Campa
Alessandro
A
Dini
Valentina
V
Esposito
Giuseppe
G
Furusawa
Yoshiya
Y
Simone
Giustina
G
Sorrentino
Eugenio
E
Tabocchini
Maria Antonella
MA
D002460:Cell Line; D004247:DNA / Q000528:radiation effects*; D004249:DNA Damage; D053938:DNA Fragmentation / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D005347:Fibroblasts / Q000528:radiation effects*; D020450:Heavy Ions; D006801:Humans; D007501:Iron; D011829:Radiation Dosage
D004247:DNA; D007501:Iron