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Long Term Effects of Heavy Ion Radiation on Bone Loss in Mice.  E.W. Livingston¹, T.A. Bateman¹.  ¹Dept. of Bioengineering, Clemson University, Clemson, SC.

   On current missions to the International Space Station, astronauts lose up to 2 percent of their bone mass per month due to the microgravity environment of space.  On future exploratory missions to the moon and Mars, exposure to ionizing radiation from cosmic rays and solar particle events has the potential to compound this bone loss through uncoupled activation of osteoclasts.  Of interest to this study is cosmic radiation in the form of heavy ions.  Heavy ions generally have higher energy levels than protons or photons and are potentially more damaging to tissue.  Prior work has shown significant bone degradation in mice in the moderate term (4 months) following exposure to both photon and particle (protons, heavy ions) radiation at doses relevant to space flight (2 Gy).  However, the longer-term effects have yet to be examined.  The purpose of this study is to examine the late effects of exposure to ionizing radiation on bone mass, with the primary focus on high-LET iron particles.  Mice (CBA/CaJ) were exposed to iron ion radiation (Brookhaven National Laboratory) at doses of 0, 10, 20, 40, and 100 cGy at ages ranging from 9 to 11 weeks of age.  The mice were sacrificed two years post-irradiation and the left hind limb was collected for analysis using micro-computed tomography (microCT).  The tibiae are currently being analyzed to determine radiation effects on bone microarchitecture.  Preliminary results show no differences (p>0.05) in trabecular volume fraction or trabecular thickness. This might suggest that the bone loss previously observed at 4 months post-irradiation has recovered after two years, or that CBA/CaJ mice are less susceptible to radiation-induced bone loss than C57BL/6 mice. Further analysis of these data with the addition of trabecular number, trabecular spacing, and connectivity density is ongoing, and will be used to more effectively quantify the long-term effects on bone of heavy ion radiation exposure.

(Supported by NSBRI through NASA NCC9-58, Procter and Gamble Pharmaceuticals and South Carolina Space Grant/NASA EPSCoR)