Decreased thyroid peroxidase expression in cultured thyrocytes after external gamma irradiation

Morphological and functional changes in rat thyroid gland after a year following chronic exposure to low and intermediate doses of γ-radiation

INTRODUCTION

Thyroid function depends on iodine uptake by the body as well as on exposure to various harmful environmental hazards (stress, ionizing radiation).

AIM

The aim of the work was to assess the effect of exposure to low and intermediate doses of external γ-radiation on the thyroid structure and function in young female rats at remote periods after radiation.

MATERIALS AND METHODS

Forty female rats were used to study remote effects of external γ-radiation exposure during 20 d (at daily doses of 0.1, 0.25 and 0.5 Gy) on the functional activity (levels of thyroid hormones, iodine metabolism) and the morphological structure of the rat thyroid) after 12 months following the radiation exposure.

RESULTS

An increase in thyroid mass and a decrease in total thyroid protein concentration along with a reduction of blood T3 and T4 was shown only in rat groups exposed to 0.25 and 0.5 Gy. Both the concentration of total iodine and its protein-bound fraction (1.2-1.4 fold, p < .01) and the protein-bound to total iodine ratio were decreased in the thyroids of all irradiated animals. The 0.1-Gy group showed elevated thyroperoxidase (TPO) activity along with increased catalase activity, which may indicate the activation of iodine oxidation by thyrocytes. Only the 0.5-Gy group demonstrated reduced urinary excretion of iodine (2.1 fold, p < .01).The reduction of thyroid function at radiation doses of 0.25 and 0.5 Gy was characterized by a microfollicular structure and the development of atrophic changes in the parenchyma, desquamation of thyroid epithelium and an increase in epithelium proliferation. The diameter of the thyrocyte nuclei was increased in rats exposed to 0.25 and 0.5 Gy, which indicates functional tension of thyrocytes.

CONCLUSION

Our research shows that after a year, the exposure to external γ-radiation of 0.1, 0.25 and 0.5-Gy caused changes in the structure and function of the rat thyroid which are manifested by the development of hypothyroiditis (0.5 Gy), 'subclinical' hypothyroiditis (0.25 Gy) and functional tension of thyrocytes. The mechanisms of thyroid dysfunction - impaired- uptake of iodine and its organification against the background of activation of free radical processes - suggest disturbances in the function of the sodium/iodide symporter (NIS), TPO and thyroglobulin synthesis. In contrast to the intermediate doses, the effects of the 0.1-Gy dose were mostly found at the remote periods compared to the earlier periods (180 days).

Long-term transcriptomic and proteomic effects in Sprague Dawley rat thyroid and plasma after internal low dose 131I exposure

Background

Radioiodide (¹³¹I) is commonly used to treat thyroid cancer and hyperthyroidis.¹³¹I released during nuclear accidents, have resulted in increased incidence of thyroid cancer in children. Therefore, a better understanding of underlying cellular mechanisms behind ¹³¹I exposure is of great clinical and radiation protection interest. The aim of this work was to study the long-term dose-related effects of ¹³¹I exposure in thyroid tissue and plasma in young rats and identify potential biomarkers.

Materials and methods

Male Sprague Dawley rats (5-week-old) were i.v. injected with 0.5, 5.0, 50 or 500 kBq ¹³¹I (D_thyroid ca 1–1000 mGy), and killed after nine months at which time the thyroid and blood samples were collected. Gene expression microarray analysis (thyroid samples) and LC-MS/MS analysis (thyroid and plasma samples) were performed to assess differential gene and protein expression profiles in treated and corresponding untreated control samples. Bioinformatics analyses were performed using the DAVID functional annotation tool and Ingenuity Pathway Analysis (IPA). The gene expression microarray data and LC-MS/MS data were validated using qRT-PCR and ELISA, respectively.

Results

Nine ¹³¹I exposure-related candidate biomarkers (transcripts: Afp and RT1-Bb, and proteins: ARF3, DLD, IKBKB, NONO, RAB6A, RPN2, and SLC25A5) were identified in thyroid tissue. Two dose-related protein candidate biomarkers were identified in thyroid (APRT and LDHA) and two in plasma (DSG4 and TGM3). Candidate biomarkers for thyroid function included the ACADL and SORBS2 (all activities), TPO and TG proteins (low activities). ¹³¹I exposure was shown to have a profound effect on metabolism, immune system, apoptosis and cell death. Furthermore, several signalling pathways essential for normal cellular function (actin cytoskeleton signalling, HGF signalling, NRF2-mediated oxidative stress, integrin signalling, calcium signalling) were also significantly regulated.

Conclusion

Exposure-related and dose-related effects on gene and protein expression generated few expression patterns useful as biomarkers for thyroid function and cancer.

Radiation and Thyroid Cancer

Radiation-induced damage is a complex network of interlinked signaling pathways, which may result in apoptosis, cell cycle arrest, DNA repair, and cancer. The development of thyroid cancer in response to radiation, from nuclear catastrophes to chemotherapy, has long been an object of study. A basic overview of the ionizing and non-ionizing radiation effects of the sensitivity of the thyroid gland on radiation and cancer development has been provided. In this review, we focus our attention on experiments in cell cultures exposed to ionizing radiation, ultraviolet light, and proton beams. Studies on the involvement of specific genes, proteins, and lipids are also reported. This review also describes how lipids are regulated in response to the radiation-induced damage and how they are involved in thyroid cancer etiology, invasion, and migration and how they can be used as both diagnostic markers and drug targets.