Radiation Risk To Low Fluences of Alpha Particles May Be Greater Than We Thought
Center for Radiological Research, College of Physicians and Surgeons and Environmental Health Sciences, School of Public Health, Columbia University August 2001

This study provides clear evidence that a single alpha particle can induce mutations and chromosome aberrations in cells that received no direct radiation exposure to their DNA. These findings imply that the target for radiation-induced genetic damage is larger than an individual cell. The observation is important in formulating risk assessment models because, for alpha particles, a cell cannot receive a dose lower than a single traversal and these hit cells are a minority population in lung tissue exposed to environmental radon.

The observation that irradiation of as few as 10% of a cell population results in a mutagenic yield similar to that when all of the cells in the population are hit indicates that low dose alpha particle irradiation can induce a huge bystander mutagenic response in neighboring cells not directly traversed by alpha particles. These results are of considerable importance in reassessing the potential genotoxic effect of low dose radiation and suggest that the assumption of direct proportionality in radiation may significantly underestimate the risk.

Induction of a Bystander Mutagenic Effect of Alpha Particles in Mammalian Cells
Center for Radiological Research, College of Physicians and Surgeons and Environmental Health Sciences, School of Public Health, Columbia University October 1, 1999

Using a precision charged particle microbeam, we show here that irradiation of 20% of randomly selected AL cells with 20 alpha particles each results in a mutant fraction that is 3-fold higher than expected, assuming no bystander modulation effect. Furthermore, analysis by multiplex PCR shows that the types of mutants induced are significantly different from those of spontaneous origin. Pretreatment of cells with the radical scavenger DMSO had no effect on the mutagenic incidence. In contrast, cells pretreated with a 40 mM dose of lindane, which inhibits cell– cell communication, significantly de-creased the mutant yield. The doses of DMSO and lindane used in these experiments are nontoxic and nonmutagenic.

We further examined the mutagenic yield when 5–10% of randomly selected cells were irradiated with 20 alpha particles each. Results showed, likewise, a higher mutant yield than expected assuming no by-stander effects.

Our studies provide clear evidence that irradiated cells can induce a bystander mutagenic response in neighboring cells not directly traversed by alpha particles and that cell to cell communication process play a critical role in mediating the by-stander phenomenon.