Genotoxicity of Therapeutic Dose of $^{131}I$ Analyzed by Micronuclei Test in the Mouse Bone Marrow

Background Radioiodine (), a major component of nuclear fallout and a valuable therapeutic agent for thyrotoxicosis and thyroid cancer, has been regarded as a mutagen or a carcinogen without any convincing evidence. To evaluate the genotoxicity of radioiodine () we performed a micronuclei test in mice bone marrow. Materials and methods : Mice (ICR strain, ) were divided to 4 groups: control, group 1 (0.17 mCi/kg, usual therapeutic dose for thyrotoxicosis), group 2 (1.67 mCi/kg, usual therapeutic dose for thyroid cancer), and group 3 (16.67 mCi/kg, usual accumulated dose causing bone marrow suppression). was administered intraperitoneally. Ten mice of each group were sacrificed at days 1 and 3. Bone marrow were smeared and stained with May-Grunwald Giemsa method. One thou-sand polychromatic erythrocytes (PCE) and normochromatic erythrocytes (NCE) were counted under the light microscope, and the number of micronucleated PCEs were recorded. Results : The frequency of micronuclei in PCE (and NCE in parenthesis) in the control group was ()% in day 1 and ()% in day 3. Those in group 1 was ()% in day 1 and ()% in day 3. Micronuclei was noted in ()% in day 1 and ()% in day 3 in group 2, and in ()% in day 1 and ()% in day 3 in group 3. There was no difference in the frequency of micronuclei between each groups (p> 0.05). Conclusion : Radioiodine () did not cause any genotoxicity in mice bone marrow even at the large dose (16.67 mCi/kg).