Effect of LET on the yield and quality of chromosomal damage in metaphase cells: a time-course study

To investigate further the effect of linear energy transfer (LET) on the yield and quality of aberrations at different post-irradiation sampling times.

V79 G(1)-cells were exposed to either 10.6 MeV u-1 Ne ions (360 keV microm-1) or 11.1 MeV u-1 Kr ions (3980 keV microm-1) and chromosomal damage was measured in metaphase cells at several 2-h sampling intervals up to 30 h post-irradiation. To differentiate between cells in the first and second post-irradiation cycle, the fluorescence-plus-Giemsa technique was applied.

In both experiments, an increase in the yield of aberrant cells as well as the number of aberrations per cell was observed in first- and second-cycle metaphases. Yet, the increase in the number of aberrations per cells was more pronounced for Kr ions and at comparable fluences Kr ions produced more aberrations than Ne ions. Because no sampling time was representative for the whole cell population, the total amount of Ne and Kr ion-induced chromosomal damage was determined by means of a mathematical approach and used for the comparison of data. Furthermore, in accordance with previous studies, LET-dependent changes in the spectrum of aberration types were detected, i.e. with increasing LET a higher fraction of chromatid-type aberrations was observed, although cells had been exposed in G1. In addition, more chromosomal breaks and less exchange-type aberrations were found.

The observation that cell-cycle progression is related to the amount of aberrations harboured by a cell demonstrates that the routinely applied method to measure aberration frequencies in metaphase cells at only one post-irradiation sampling time will unavoidably result in an under- or overestimation of the cytogenetic effects of particles. Consequently, for a meaningful quantification of chromosomal damage, multiple fixation regimes should be used so that the complete time-course of aberrations can be taken into account. Moreover, to avoid bias, all aberration types should be recorded and included in the analysis since the aberration spectrum changes with LET.