Effects of low fluences of radiations found in space on cellular systems

In recent years, there has been a large increase in the amount of space-related radiation biology research being conducted. This review will discuss selected issues related to cellular responses to the types of radiations found in space, with emphasis on comparison of cellular effects from high versus low linear energy transfer (LET) radiations and on effects that might be expected to predominate at the low radiation fluences characteristic of space, e.g., bystander effects and adaptive responses.

Space radiation is unique and complex, being composed of galactic cosmic rays and solar particles. Not surprisingly, space radiation biology is also unique and complex. Responses in cells traversed by high atomic number, high energy (HZE) particles are different, at least in part, from the responses of cells exposed to low LET photons not just quantitatively but also qualitatively. This is illustrated by discussion of four sets of data - clustering of DNA damages, foci of DNA repair-related proteins, chromosome aberrations and gene expression. 'Non-targeted' effects, particularly bystander responses, may have increased importance in cellular responses to space radiation because of the very low fluences and fluence rates as well as the non-homogeneous dose distributions from HZE particles compared to the more homogeneous distributions of the photon radiations usually encountered on Earth. Likewise adaptive responses could be expected to play a role in cellular damages at the low particle fluences characteristic of space. The growing number of ground-based studies being performed with energetic protons and heavy ions should lead to greatly expanded knowledge of the impact of the space radiation environment on astronauts.