Long-term changes in rat hematopoietic and other physiological systems after high-energy iron ion irradiation

Purpose: To assess the long-term consequences of high-linear energy transfer (LET) iron ion radiation on immune and other critical body systems in the context of assessing potential effects astronauts may experience during exploratory missions. Materials and methods: Sprague-Dawley rats were nearly whole-body irradiated with 56-Fe (5 GeV/n) to total doses of 0, 1, 2, and 4 Gray (Gy) and euthanized 9 months post-exposure for analyses. Results: Irradiated groups consistently had low body mass. Numbers of circulating white blood cells (WBC), lymphocytes and monocytes were lower in the 2 Gy group compared to 0 Gy (p < 0.05); a trend for low granulocytes was also noted. Red blood cell counts, hemoglobin, and hematocrit were decreased in irradiated animals (p < 0.05), whereas platelet counts and volume were unaffected. In the spleen, WBC counts and DNA synthesis by T cells were similar among groups and there were no differences in secreted interferon-gamma and interleukin-6. However, trends were noted for increased splenocyte capacity to secrete tumor necrosis factor-alpha and increased level of vascular endothelial cell growth factor in plasma. One or more of the irradiated groups had significant (p < 0.05) aberrations in several blood chemistry parameters associated with liver and kidney function. Conclusion: The data show that exposure to 56-Fe radiation induced pathological changes in important body systems long after exposure.