Analysis of α-particle-induced chromosomal aberrations by chemically-induced PCC. Elaboration of dose-effect curves

In a similar way to high-dose exposures to low-LET radiations, cells show difficulties reaching mitosis after high-LET radiation exposure. For this reason, techniques have been proposed that are able to analyze chromosome aberrations in interphase by prematurely condensing the chromosomes (PCC-techniques). Few dose-effect curves for high-LET radiation types have been reported, and none for α-particles. The aim of this study was to evaluate, by chemically-induced PCC, the chromosome aberrations induced by several doses of α-particles. Monolayers of peripheral lymphocytes were exposed to an α-source of Americium-241 with a mean energy entering the cells of 2.7 MeV. Lymphocytes were exposed to 10 doses, from 0-2.5 Gy, and then cultured for 48 h. Colcemid and Calyculin-A were added at 24 and 1 h before harvesting, respectively. During microscope analysis, chromosome rings and extra chromosome pieces were scored in G2/M-PCC and M cells, while dicentric chromosomes were only scored in M cells. As the dose increased, fewer cells were able to reach mitosis and the proportion of G2/M-PCC cells increased. Chromosome rings were hardly observed in M cells when compared to G2/M-PCC cells. Extra fragments were more frequent than rings in both G2/M-PCC and M cells, but with lower frequencies than in G2/M-PCC cells. The distribution of dicentrics and extra fragments showed a clear overdispersion; this was not so evident for rings. The dose-effect curves obtained fitted very well to a linear model. Damaged cells after α-particle irradiation show more difficulties in reaching mitosis than cells exposed to γ-rays. After α-particle irradiation the frequency of all the chromosome aberrations considered increased linearly with the dose, and α-particles clearly produced more dicentrics and extra chromosome pieces with respect to γ-rays. After α-particle exposure, the existence of extra chromosome fragments in PCC cells seems to be a good candidate for use as a biomarker for dose assessment. However, the observed frequencies of different types of chromosomal aberrations could be influenced by some methodological aspects; for this reason, and in order to avoid possible methodological bias, standardization of the technique will be desirable.