The Use of Low‐Dose Radiation Pre‐Treatments as a Potential Countermeasure to Galactic Cosmic Radiation Exposure

Abstract

Space exploration involves many dangers, including radiation exposure from galactic cosmic radiation (GCR). This includes high energy protons and heavy ionizing ions such as 56Fe, 28Si, and 16O. NASA has defined GCR as a carcinogenic risk for long‐duration space missions. To date no clear strategy has been developed to counter chronic GCR exposure. We hypothesize that preconditioning cells with low levels of radiation will be protective from subsequent higher radiation exposures. H9C2 cells maintained in culture were pretreated with 0, 0.1, or 0.5 Gy X‐rays using a RadSource 2000 Irradiator. The challenge radiation treatment consisted of either 8 Gy X‐ray or 75cGy of GCR, using a 5 Ion GCRsim protocol. To determine cell health, the cell doubling time assay was used. 10000 cells from each treatment group were put into wells of a 24 well plate and maintained for 48‐72 hours. Following harvest, cells were counted using a flow cytometer. The 8 Gy X‐ray challenge alone significantly (p<.05) increased cell doubling time compared to the no radiation control group. The radiation pre‐treatment groups ameliorated the 8 Gy X‐ray induced increases in cell doubling time and there was no difference compared to the no radiation control group. 75 cGy GCR challenge alone significantly increased cell doubling time compared to the no radiation group. Following the 75cGy challenge, only the 0.5 Gy pre‐treatment ameliorated the 75cGy induced increases in cell doubling time. The cell doubling time protocol measures the amount of time require for a cell to undergo mitosis. It is directly influence by DNA integrity as well as mitochondrial and cellular function. DNA damage or pathologic oxidant stress will delay the replicative functions. As such this is a physiologic measure of the cell wellbeing. Our results suggested that pretreatment with low dose X‐rays enhanced cellular resiliency by inducing an adaptive response which offered a small but significant protection against a following higher radiation challenge. Although perhaps not a practical countermeasure, these findings may serve to offer insight to cell signaling pathways activated in response to low dose irradiation and that might be targeted as a potential countermeasure.