Effects of Space Radiation on Mammalian Cells

Abstract

In an era of increasing space mission durations, radiation exposure may be a major impediment to ensuring human health and wellness. There are several forms of radiation found in space not present on Earth, generally comprised of higher-energy particles. Microscopic dose distribution is a major difference between sparsely and densely ionizing radiation. The ionization patterns and resulting biological effects on molecules, cells, and tissues are distinct from typical low linear energy transfer terrestrial radiation which is largely X-rays and gamma rays. In general, radiation-related effects at the cellular level are grouped into direct or indirect DNA damage or non-DNA damage. Biophysical models have shown that high linear energy transfer radiation produces more complex DNA breaks and rearrangements and high rates of misrepair. Metastatic tumor rates and grade are higher than with lower-energy radiation exposures. Indirect effects relate to reactive oxygen species generated through reactions with water. Bystander effects occur in cells that were not themselves irradiated as a result of disrupted cell signaling mechanisms. Microgravity alone has also shown cell line mutations and may confound the effects of radiation. Other complicating factors include possible adaptive responses to low-dose radiation, and countermeasures such as antioxidants meant to protect cells by rescuing them from apoptosis then allow the survival of damaged cells eventually initiating tumor progression depending on the radiation dose. Despite decades of data gathering related to radiation physics, dosimetry, and radiobiology, knowledge gaps outweigh our understanding of space radiation.