Impact of radiation quality on the spectrum of induced chromosome exchangeaberrations

Purpose: To study the impact of radiation quality on the spectrum of chromo some exchange aberrations in human lymphocytes using chromosome arm-specifi c and telomeric probes. The analysis is focused on: (1) incomplete exchange s, (2) interstitial fragments, (3) interarm intrachanges and (1) the comple xity of the aberration patterns. The present data after neutron exposure ar e compared vith previously obtained data after X-irradiation. Materials and methods: Isolated human lymphocytes from three donors were ir radiated with 1 MeV fast neutrons (0.25, 0.5, 1.0, 1.5, 2.0 Gy). Analysis, vas performed on first Post-irradiation metaphases with arm-specific probes For chromosome 1 in combination With a pan-centromeric probe, or with telo meric and centromeric PNA probes. Results: In comparsion with X-rays, exposure to neutrons leads to: (1) simi lar frequencies of incomplete exchanges or terminal deletions, (2) a signif icantly higher induction of both inter- and intraarm intrachanges, (3) a hi gher proportion of complex aberrations, and (4) aberrations with a higher d egree of complexity, i.e. derived from more chromosome breaks which interac t more frequently in a non-reciprocal fashion. Essentially no dose dependen ce,vas found for the yield ratios between the various types of chromosomal aberrations, Conclusions: Despite the reduced rejoining efficiency of DNA double-strand breaks induced by high-LET radiation, exposure to neutrons does not lead to enhanced levels of unrejoined chromosome breaks that can be observed as in complete exchanges in cells that have reached mitosis. Proximity effects ar e more pronounced after densely ionizing radiation than alter sparsely ioni zing radiation. clustered damage produced by neutron tracks results in a hi gh proportion of complex aberrations and in non-reciprocal interactions of chromosome breaks. Most of the exchanges occur within one neutron track and little interaction seems to take place between the breaks formed in differ ent tracks.