3149 - Effect of Acute High Dose TBI on RBC Dysfunction and Erythropoiesis in C57BL/6J Mice

Purpose/Objective(s):

High dose total body irradiation (TBI) leads to the development of acute radiation syndrome (ARS), a life-threatening condition characterized by severe neutropenia, thrombocytopenia and anemia resulting from radiation-induced ablation of bone marrow. While drugs have been approved for treatment of radiation-induced neutropenia and thrombocytopenia, there are no approved drugs for treating radiation-induced anemia. Further, our current understanding of anemia in ARS following high dose TBI has not elucidated the exact mechanisms driving red blood cell (RBC) injury. We hypothesize that high dose TBI drives intravascular hemolysis, extravascular hemolysis, or a combination of both, resulting in acute anemia followed by a compensatory erythropoietic response.

Materials/Methods:

To study the hematological effects of high dose ionizing radiation, C57BL/6J mice were exposed to a single uniform total body dose of x-ray irradiation of 7.5 Gy, a highly lethal dose with 100% mortality by day 10. Mice were euthanized at different timepoints following irradiation for blood and tissue collection. Following euthanasia, necropsy was conducted to visualize gross pathology of organs and potential hemorrhaging. Complete blood count analysis was performed on whole blood and RBC specific assays, including scanning electron microscopy, were performed to assess membrane morphology. Iron distribution and oxidative stress markers were analyzed by immunohistochemistry. Finally, plasma markers of erythropoiesis, including erythropoietin (EPO), erythroferrone (ERFE) and hepcidin were analyzed to study compensatory response.

Results:

The cumulative data suggest that following TBI, gastrointestinal (GI) hemorrhage develops, which was consistent with a precipitous drop in platelets. RBC clearance by spleen macrophages and liver Kupffer cells also contributed to the development of severe anemia. In response to the acute anemia, EPO increased. However, regulation of proteins downstream of EPO that modulate iron absorption, such as ERFE and hepcidin, were incongruous to the renal response to anemia.

Conclusion:

Anemia was first described as a major consequence of high dose radiation following the atomic bomb detonations in Hiroshima and Nagasaki but has not received extensive study in subsequent decades. We show that exposure to high dose TBI induces GI hemorrhage and extravascular hemolysis in the spleen and liver, leading to acute anemia. However, compensatory erythropoiesis through the EPO pathway was dysregulated and the mice were unable to overcome the radiation-induced hematologic damage. These findings provide novel insight into the mechanisms driving anemia following irradiation. Continued investigation will lead to the identification of potential targets for drug development to treat radiation-induced anemia in the clinic and following a mass casualty radiologic/nuclear event.