Radiation in Space: The Biology

Abstract

The galactic cosmic radiation (GCR) results constant exposure of astronauts to charged particles of various energies at a low-dose rate. A traversal of a charged particle through a cell nucleus can result in (complex) DNA damage which initiates the DNA damage response (DDR). During this response, the cell might arrest in the cell cycle in order to gain time for DNA repair. Depending on damage severity, cell type, and other factors, different outcomes such as cell death, premature differentiation, senescence, or chromosomal aberrations are possible. In addition to effects on the main target molecule, the DNA, non-targeted effects contribute to overall outcome for a GCR exposed organism. Compared to X- or γ-rays, heavy charged particles can have a high relative biological effectiveness (RBE) for inducing different biological outcomes, including cancer-relevant outcomes and cancer in rodents. Primarily, late tissue sequels like genetic alterations, cancer and non-cancer effects, i.e., cataracts and degenerative diseases, e.g., of the central nervous system, are potential risks for space travelers. Cataracts were observed to occur with earlier onset and more frequently in astronauts exposed to even low doses of GCR. In addition, the continuously existing risk of acute exposure to high proton fluxes during a solar particle events (SPE) implies to threaten immediate survival of the astronauts in case of insufficient shielding by eliciting the acute radiation syndrome (ARS).