PERSISTENCE OF RADIATION-INDUCED TRANSLOCATIONS IN HUMAN PERIPHERAL-BLOOD DETERMINED BY CHROMOSOME PAINTING

We have investigated the persistence of translocations and other types of chromosome damage with time using human peripheral blood acutely e xposed in vitro to Cs-137 gamma rays at doses ranging from 0.5 to 4 Gy , Freshly drawn blood from one donor was irradiated and metaphase chro mosomes were prepared 2 to 7 days after exposure. Chromosomes 1, 2 and 4 were painted red-orange and chromosomes 3, 5 and 6 were painted gre en by fluorescence in situ hybridization (FISH) using ''semi-directly' ' labeled whole-chromosome painting probes. This type of labeling comb ines direct and indirect labeling and showed significant advantages ov er both these other methods. All types of structural chromosome aberra tions were classified by the Protocol for Aberration Identification an d Nomenclature Terminology (PAINT) system. The yields of dicentric chr omosomes, acentric fragments and ring chromosomes diminished with time as expected. Translocations exhibited greater persistence but showed a clear and statistically significant reduction in frequency at all do ses. The mathematical model suggested that the translocation frequenci es would reach a plateau of approximately 4, 15, 51, 106 and 179 trans locations per 100 cell equivalents after irradiation with 0.5, 1, 2, 3 and 4 Gy, respectively. When translocations were classified by the co nventional system, an analysis of the distribution of translocations a nd dicentrics per cell indicated that both types of exchanges were Poi sson-distributed 48 h postirradiation. However, cells bearing transloc ations have a higher possibility of having dicentrics than cells witho ut translocations, These findings suggest that dicentrics may contribu te to a decline of translocation frequencies with time, and that some translocations are not completely persistent. The results obtained her e using human blood exposed in vitro may influence the use of transloc ations as a retrospective biodosimeter of exposure to ionizing radiati on in humans. (C) 1998 by Radiation Research Society.