Cellular effects of energetic heavy ions: from DNA breaks to chromosomal rearrangements

Chromosome aberrations determined by sFISH and G-banding in lymphocytes from workers with internal deposits of plutonium

Purpose: To examine the influence of α-particle radiation exposure from internally deposited plutonium on chromosome aberration frequencies in peripheral blood lymphocytes of workers from the Sellafield nuclear facility, UK. Materials and methods: Chromosome aberration data from historical single colour fluorescence in situ hybridization (sFISH) and Giemsa banding (G-banding) analyses, together with more recent sFISH results, were assessed using common aberration analysis criteria and revised radiation dosimetry. The combined sFISH group comprised 29 men with a mean internal red bone marrow dose of 21.0 mGy and a mean external γ-ray dose of 541 mGy. The G-banding group comprised 23 men with a mean internal red bone marrow dose of 23.0 mGy and a mean external γ-ray dose of 315 mGy. Results: Observed translocation frequencies corresponded to expectations based on age and external γ-ray dose with no need to postulate a contribution from α-particle irradiation of the red bone marrow by internally deposited plutonium. Frequencies of stable cells with complex aberrations, including insertions, were similar to those in a group of controls and a group of workers with external radiation exposure only, who were studied concurrently. In a similar comparison there is some suggestion of an increase in cells with unstable complex aberrations and this may reflect recent direct exposure to circulating lymphocytes. Conclusions: Reference to in vitro dose response data for the induction of stable aberrant cells by α-particle irradiation indicates that the low red bone marrow α-particle radiation doses received by the Sellafield workers would not result in a discernible increase in translocations, thus supporting the in vivo findings. Therefore, the greater risk from occupational radiation exposure of the bone marrow resulting in viable chromosomally aberrant cells comes from, in general, much larger γ-ray exposure in comparison to α-particle exposure from plutonium.

mFISH analysis of chromosome aberrations induced in vitro by α-particle radiation: examination of dose-response relationships

A multicolored FISH (mFISH) technique was used to characterize the cytogenetic damage associated with exposure to α-particle radiation with particular emphasis on the quality and quantity that is likely to be transmitted through cell division to descendant cells. Peripheral blood lymphocytes were irradiated in vitro with (238)Pu α particles with a range of mean doses up to 936 mGy and were cultured for 47 h. The dose responses for total aberrant cells, stable and unstable cells, and cells with one simple chromosome aberration and multiple chromosome aberrations were predominantly linear for doses that resulted in cell nuclei receiving a single α-particle traversal. However, there was a decrease per unit dose in aberrant cells of all types at higher doses because of cells increasingly receiving multiple traversals. The proportion of radiation-induced aberrant cells containing multiple aberrations ranged from 48 to 74% with little evidence of dose dependency. Ninety-one percent of all cells with multiple aberrations were classified as unstable. Resolving the chromosome rearrangements into simple categories resulted in a linear dose response for dicentrics of 24.9 ± 3.3 × 10(-2) per Gy. The predominant aberration in stable transmissible cells was a single translocation with a dose response for predominantly single hit cell nuclei of 4.1 ± 1.3 × 10(-2) per Gy. Thus, translocations are the most likely aberration to be observed in peripheral blood lymphocytes from individuals with incorporated α-emitting radionuclides resulting in long-term chronic exposure.