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Effect of Local Iron Irradiation on Trabecular Bone.  E.R. Bandstra¹, S. Judex², M.E. Vazquez³, T.A. Bateman¹

¹Dept. of Bioengineering, Clemson Univ., Clemson, SC, ²Dept. of Biomedical Engineering, State Univ. of New York at Stony Brook, ³Medical Dept., Brookhaven National Laboratory, Upton, NY.

   On long-duration exploratory missions, astronauts will be exposed to higher doses of ionizing radiation from both solar and cosmic sources. While NASA has been concerned with radiation exposure’s effect on the central nervous and immune systems, we have recently identified that spaceflight-relevant types of radiation, approaching doses astronauts will be exposed to on exploratory missions, cause profound trabecular bone loss. This study aims to investigate the effects of local (head only) irradiation on regional and systemic trabecular bone. Male C57BL/6 mice were irradiated with 1GeV/n HZE ⁵⁶Fe at 16 weeks of age at the NASA Space Radiation National Laboratory. The radiation was collimated such that the head received 2.4 Gy and the rest of the body, including humerus and tibia, received 14% (33.6 cGy) of the total dose delivered. The mice were sacrificed 8 weeks after irradiation. MicroCT analysis was performed on the trabecular bone of the proximal humerus and tibia. The humerus showed a significant 15.1% decline in trabecular volume fraction compared to the control group. However, the tibia did not show any changes compared to control (insignificant decline in trabecular volume fraction of 4%). The bone loss in the humerus, without corresponding loss in the tibia, indicates either a differential response of these bones or a greater loss in bones proximal to higher doses of radiation. Another important contribution of this study is the demonstration of bone loss in mice near peak bone mass. Our previous studies examined mice irradiated at 9 weeks of age, when the skeletal system is rapidly growing. Radiation-induced bone loss in the mature skeleton further demonstrates that this is a potential concern for astronauts on long-duration exploratory missions and should be studied to further characterize the bone loss, identify causal mechanisms and develop countermeasures. Supported by South Carolina Space Grant, Procter and Gamble, the NSBRI (NASA NCC9-58), BioServe Space Technologies (NASA NCC 8-242), and NASA NAG 9-1499 (S.J.).