Abstract
The influence of dose rate on radiation cataractogenesis has yet to be extensively studied. One recent epidemiological investigation suggested that protracted radiation exposure increases radiation-induced cataract risk: cumulative doses of radiation mostly <100 mGy received by US radiologic technologists over 5 years were associated with an increased excess hazard ratio for cataract development. However, there are few mechanistic studies to support and explain such observations. Low-dose radiation-induced DNA damage in the epithelial cells of the eye lens (LECs) has been proposed as a possible contributor to cataract formation and thus visual impairment. Here, 53BP1 foci was used as a marker of DNA damage. Unexpectedly, the number of 53BP1 foci that persisted in the mouse lens samples after γ-radiation exposure increased with decreasing dose-rate at 4 and 24 h. The C57BL/6 mice were exposed to 0.5, 1 and 2 Gy ƴ-radiation at 0.063 and 0.3 Gy/min and also 0.5 Gy at 0.014 Gy/min. This contrasts the data we obtained for peripheral blood lymphocytes collected from the same animal groups, which showed the expected reduction of residual 53BP1 foci with reducing dose-rate. These findings highlight the likely importance of dose-rate in low-dose cataract formation and, furthermore, represent the first evidence that LECs process radiation damage differently to blood lymphocytes.
Highlights
Since the International Commission on Radiological Protection (ICRP) recommended a reduction in the eye lens occupational dose limit for ionising radiation (IR) exposure in 20121 there has been a need for reliable mechanistic evidence to underpin the recommendations and subsequent changes in the IAEA and EU Basic Safety Standards which recently came into force[2]
Analysis of the peripheral blood lymphocyte samples was performed firstly to compare with LECs, but secondly to confirm the dose rate effects seen in previous mouse studies[38]
Residual 53BP1 foci were scored at 24 h post-exposure for both 0.5 and 1 Gy doses at both 0.3 and 0.063 Gy/min dose rates and plotted with standard error (SE) bars (Fig. 2)
Summary
Since the International Commission on Radiological Protection (ICRP) recommended a reduction in the eye lens occupational dose limit for ionising radiation (IR) exposure in 20121 there has been a need for reliable mechanistic evidence to underpin the recommendations and subsequent changes in the IAEA and EU Basic Safety Standards which recently came into force[2]. A very recently published epidemiological study, by Little et al.[9], has suggested an excess hazard ratio of 0.69 (0.27–1.16) per Gy of IR to the formation of cataract in radiologic technologists following cumulative occupational exposures to low doses (mostly < 100 mGy) accumulated over an average 5-year lagged eye lens absorbed dose[9] (using self-reported cataract history as an endpoint). This excess hazard ratio was significantly different from the lowest dose exposure cases (
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