Simultaneous Exposure of Cultured Human Lymphoblastic Cells to Simulated Microgravity and Radiation Increases Chromosome Aberrations.

During space travel, humans are continuously exposed to two major environmental stresses, microgravity (µG) and space radiation. One of the fundamental questions is whether the two stressors are interactive. For over half a century, many studies were carried out in space, as well as using devices that simulated µG on the ground to investigate gravity effects on cells and organisms, and we have gained insights into how living organisms respond to µG. However, our knowledge on how to assess and manage human health risks in long-term mission to the Moon or Mars is drastically limited. For example, little information is available on how cells respond to simultaneous exposure to space radiation and µG. In this study, we analyzed the frequencies of chromosome aberrations (CA) in cultured human lymphoblastic TK6 cells exposed to X-ray or carbon ion under the simulated µG conditions. A higher frequency of both simple and complex types of CA were observed in cells exposed to radiation and µG simultaneously compared to CA frequency in cells exposed to radiation only. Our study shows that the dose response data on space radiation obtained at the 1G condition could lead to the underestimation of astronauts' potential risk for health deterioration, including cancer. This study also emphasizes the importance of obtaining data on the molecular and cellular responses to irradiation under µG conditions.

Increased Chromosome Aberrations in Cells Exposed Simultaneously to Simulated Microgravity and Radiation.

Space radiation and microgravity (µG) are two major environmental stressors for humans in space travel. One of the fundamental questions in space biology research is whether the combined effects of µG and exposure to cosmic radiation are interactive. While studies addressing this question have been carried out for half a century in space or using simulated µG on the ground, the reported results are ambiguous. For the assessment and management of human health risks in future Moon and Mars missions, it is necessary to obtain more basic data on the molecular and cellular responses to the combined effects of radiation and µG. Recently we incorporated a µG⁻irradiation system consisting of a 3D clinostat synchronized to a carbon-ion or X-ray irradiation system. Our new experimental setup allows us to avoid stopping clinostat rotation during irradiation, which was required in all other previous experiments. Using this system, human fibroblasts were exposed to X-rays or carbon ions under the simulated µG condition, and chromosomes were collected with the premature chromosome condensation method in the first mitosis. Chromosome aberrations (CA) were quantified by the 3-color fluorescent in situ hybridization (FISH) method. Cells exposed to irradiation under the simulated µG condition showed a higher frequency of both simple and complex types of CA compared to cells irradiated under the static condition by either X-rays or carbon ions.