Evaluation of the cytogenetic effects of 131I preceded by recombinant human thyrotropin (rhTSH) in peripheral lymphocytes of Wistar rats

Abstract

The present study was carried out to investigate the cytogenetic effects of therapeutic exposure to radioiodine preceded by rhTSH in an animal model. Three groups of Wistar rats (n = 6) were used: one group was treated only with (131)I (11.1 MBq/animal); the other two groups received rhTSH (1.2 mug/rat of either Thyrogen or rhTSH-IPEN, respectively) 24 h before administration of radioiodine. The percentage of lymphocytes with chromosome aberrations and the average number of aberrations and of dicentrics per cell were determined on blood samples collected 24 h, 7 and 30 days after administration of (131)I. The data show that the treatment with radioiodine alone or associated with rhTSH resulted in a greater quantity of chromosome alterations in relation to basal values after 24 h, with a gradual decline after 7 and 30 days of treatment. An increase in chromosome alterations was also seen after rhTSH treatment alone. Neither of the treatments, i.e., with (131)I alone or associated with hormone, resulted in an aneugenic effect or influenced the kinetics of cellular proliferation in rat blood lymphocytes. There was no significant difference between the cytogenetic effects of Thyrogen and rhTSH-IPEN treatment. These data suggest that the treatment with radioiodine, associated or not with rhTSH, affects to a limited extent a relatively small number of cells although the occurrence of late stochastic effects could not be discarded.

Mutagenicity of diagnostic and therapeutical doses of radiopharmaceutical iodine-131 in Wistar rats

“…Chromosomal aberrations observed in this study, as well as those found by Silva et al (2008), may be partly a consequence of the combination of 131 I accumulation in the thyroid gland, which acts as an internal source of irradiation, with the concomitant loss of selectivity of damaged bone marrow cells. One possible explanation for this phenomenon is the low penetration energy of b particles, which may only affect a small number of cells but can deposit a fraction of the energy heterogeneously in the nuclei, thereby generating various types of damage in DNA.…”

“…The study by Silva et al (2008) also had a larger number of chromosomal aberrations in rat lymphocytes after 24 h of treatment with 0.30 mCi of 131 I, with gradual decline after 7 and 30 days. Similar data were reported by Watanabe et al (1998) using the micronucleus cell test with lymphocytes from 25 patients treated with 0.10 Ci of 131 I, in which the micronuclei frequency significantly increased after therapy and decreased after 2 weeks before reaching the baseline.…”

“…The data from several investigations are contradictory regarding the increase (Gutiérrez et al 1997(Gutiérrez et al , 1998Gil et al 2000a) or decrease (Watanabe et al 1998;Puerto et al 2000;Ballardin et al 2002;Silva et al 2008) of DNA damage induced by 131 I concerning the time elapsed after exposure to radiation. In this study, the treatment with 25 lCi for 24 h and 5 days did not produce statistically different results.…”

“…Studies conducted in several test systems with various doses of radioiodine, different than those tested here, showed high frequencies of chromosomal aberrations (Puerto et al 2000;Silva et al 2008) and micronuclei (Ballardin et al 2002;Watanabe et al 2004;Grawé et al 2005;Joseph et al 2009). The chromosomal damage induced by radioiodine exposure predisposes individuals to a future risk of developing cancer (Federico et al 2008).…”

Radioprotective effect of the Barbados Cherry (Malpighia glabra L.) against radiopharmaceutical Iodine-131 in Wistar rats in vivo

“…Several studies have confirmed the mutagenic activity of different doses of 131I based on evidence from the induction of micronuclei [2,3] and the presence of chromosomal aberrations [4,5]. …”