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Effects of Low Dose Ionizing Radiation on Bone Metabolism in Rats.  L. Tirado, J.S. Willey, T.A. Bateman. Department of Bioengineering, Clemson University, Clemson, SC.

   The dangers associated with the space environment must be better understood as we prepare for long-duration exploratory missions. Space radiation (protons, heavy ions, and gamma/x-rays) represent a chief environmental challenge astronauts must face. In space, gamma radiation, produced as a secondary result of heavy ions striking shielding material, is of concern to astronauts. During these long-duration space missions, many biomedical problems could result from radiation exposure. Bone loss is being investigated as one of these problems. It is important to understand complications to osseous tissue and ultimately develop countermeasures to ensure astronaut and mission success. 

   To characterize the time-course of bone loss following radiation exposure, two groups of nine-week-old female Sprague Dawley rats were examined, n = 10 per group. The first group received no radiation and served as the control group. The second group received 2 Gray (Gy) of x-rays applied to the whole body. Blood was collected 3, 7, 10, 14, 21 and 28 days after exposure. Enzyme-linked immunosorbent assays (ELISAs) were used to measure the levels of bone-relevant proteins after irradiation. During the bone remodeling cycle, bone is broken down by osteoclasts and reformed by osteoblasts. Two important proteins are secreted by these cells during bone metabolism: osteoclasts secrete tartrate-resistant acid phosphotase 5b (TRAP 5b) while osteoblasts secrete osteocalcin. Therefore, time-course measurement of these proteins will examine changes in the bone remodeling process, providing insight into the nature of radiation-induced bone loss. Preliminary analysis reveals that on Day 3, TRAP 5b levels of the whole-body group were significantly increased compared to the control group. However, on Day 6, there was no statistical difference between the levels in any of the groups. This suggests bone resorption is a relatively early response following radiation exposure.

(Supported by Procter & Gamble Pharmaceuticals and the SC LIFE Undergraduate Research Grant from Howard Hughes Medical Institute.)