Iron-58 and neutron activation analysis: a non-radioactive method for tracing hemoglobin iron

To develop a non-radioisotopic alternative to radioactive Fe-59 as a hemoglobin iron tracer, we evaluated Fe-58 and neutron activation analysis (NAA). Upon irradiation with thermal neutrons, stable isotope Fe-58 is converted to radioactive Fe-59 through (n,gamma) neutron reaction; its radioactivity measured by a gamma counter is proportional to the original Fe-58 present. Organ samples from rats infused with Hb or saline were analyzed along with a 10 mg Hb as a standard (105 nanograms of Fe-58). The measured values of Fe-58 in tissues were compared with those derived from the literature tissue iron contents. The amount of Fe-58 in normal tissue is extremely low yet detectable by NAA demonstrating high sensitivity. Measured values of Fe-58 from tissues were generally correlated well with literature derived values (e.g., brain: 0.19 and 0.15 ng/mg tissue; kidney: 0.6 and 0.7 ng/mg tissue, respectively). The results indicate that Fe-58 can be used as a non-radioactive tracer for absorption, distribution, metabolism, and distribution studies of hemoglobin-based oxygen carriers.