Susceptibility of Hematopoietic Stem Cells (CFU-s) to 55 Fe Radiation Damage

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Abstract
The susceptibility of CFU-s [hemopoietic stem cell] to radiation damage from 55Fe was examined. Irradiation emitted from 55Fe-loaded erythrocytes had no effect on erythroid colony formation during 72 h of incubation. This demonstrated the low biological radiation effect of extracellular 55Fe. Normal mouse bone marrow cell suspensions were then mixed with 55Fe-loaded bone marrow, 55FeCl3 or [55Fe]desferrioxamine. No effect on CFU-s was found after up to 1 h of incubation. When normal bone marrow mixed with [55Fe]desferrioxamine was frozen and stored at -196.degree. C, measurable damage to CFU-s progressed with increased storage time. Normal marrow mixed with stable [56Fe]desferrioxamine showed no loss of CFU-s over 13 wk storage. Direct radiation damage to CFU-s was measured by freezing bone marrow 4 or 24 h after 55Fe injection of donor mice and determining viable CFU-s after 1-60 wk. Logarithmic loss functions typical of radiation damage were observed with half times of 3.0 and 4.4 wk. In vivo 55Fe radiation dose to CFU-s was estimated using the slope of CFU-s loss curves obtained in frozen storage. It was derived that i.v. injection of mice with 1.4 mCi 55FeCl3 (approximately 80 .mu.Ci/g body wt) subjects CFU-s to damage that were ascribed to 0.37 rad/h and 0.54 rad/h after 4 and 24 h, respectively.