Chromosome Translocations, Inversions and Telomere Length for Retrospective Biodosimetry on Exposed U.S. Atomic Veterans

Abstract

It has now been over 60 years since U.S. nuclear testing was conducted in the Pacific islands and Nevada, exposing military personnel to varying levels of ionizing radiation. Actual doses are not well-established, as film badges in the 1950s had many limitations. We sought a means of independently assessing dose for comparison with historical film badge records and dose reconstruction conducted in parallel. For the purpose of quantitative retrospective biodosimetry, peripheral blood samples from 12 exposed veterans and 12 age-matched (>80 years) veteran controls were collected and evaluated for radiation-induced chromosome damage utilizing directional genomic hybridization (dGH), a cytogenomics-based methodology that facilitates simultaneous detection of translocations and inversions. Standard calibration curves were constructed from six male volunteers in their mid-20s to reflect the age range of the veterans at time of exposure. Doses were estimated for each veteran using translocation and inversion rates independently; however, combining them by a weighted-average generally improved the accuracy of dose estimations. Various confounding factors were also evaluated for potential effects on chromosome aberration frequencies. Perhaps not surprisingly, smoking and age-associated increases in background frequencies of inversions were observed. Telomere length was also measured, and inverse relationships with both age and combined weighted dose estimates were observed. Interestingly, smokers in the non-exposed control veteran cohort displayed similar telomere lengths as those in the never-smoker exposed veteran group, suggesting that chronic smoking had as much effect on telomere length as a single exposure to radioactive fallout. Taken together, we find that our approach of combined chromosome aberration-based retrospective biodosimetry provided reliable dose estimation capability, particularly on a group average basis, for exposures above statistical detection limits.

Estimation of Radiation Doses to U.S. Military Test Participants from Nuclear Testing: A Comparison of Historical Film-Badge Measurements, Dose Reconstruction and Retrospective Biodosimetry

“…More recently, chromosomal inversions (inverted segments within chromosomes) have been proposed as potential retrospective biodosimeters (33). Here, for the first time, they were investigated for reconstructing past exposures [see (12)]. Like the case for reciprocal translocations (rearrangements between chromosomes), inversions are symmetrical (i.e., they are balanced); therefore, they also persist with time.…”

“…Here, we hypothesized a priori that inclusion of inversions could improve retrospective biodosimetry for estimating exposures that took place over six decades in the past, reasoning that their persistence and higher induction rate per unit dose would be favorable for retrospective dose estimation. Furthermore, we hypothesized that changes in telomere length [e.g., shortening, see (35)] might also reflect these past radiation exposures, thereby providing insight into potential long-term biological and overall health implications [see (12)]. These considerations were the basis for the design of an assessment based on both inversions and translocations.…”

“…To identify inversions and translocations, dGH was employed using single-color whole chromosome 1, 2 and 3 paints (KromaTiD Inc., Ft. Collins, CO), and performed as described elsewhere (12,34). Over 200 metaphase spreads per military participant and 300 metaphase spreads per young adult volunteer were imaged and analyzed to establish aberration rates.…”

“…To allow the assessment of individual doses from measurements of chromosome aberration rates, dose-response curves for inversions and translocations were established by exposing whole peripheral blood ex vivo from six male volunteers in their mid-20s (similar age of exposure as the military test participants) to a range of 137 Cs gamma-ray doses and the aberration rates were assessed as a function of dose. Linear relationships were evident in all derived calibration curves [see (12)]. In simple terms, the dose to bone marrow from measurements of translocation and inversion frequencies was individually assessed using Eq.…”

“…Finally, six younger adult males (;25 years of age) were selected from the student body at Colorado State University (via response to a newspaper advertisement) to provide a blood sample from which ex vivo exposure calibration curves could be constructed for radiationinduced translocations and inversions. The age of the young adult controls was chosen to approximate the age of the military test participants at the time of their exposure [see (12)]. None were reported to be smokers.…”