Effects of ultraviolet radiation on FRTL-5 cell growth and thyroid-specific gene expression

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).

Single and combined effects of ultraviolet radiation and triclosan during the metamorphosis of Solea senegalensis

Ultraviolet radiation (UV) and triclosan (TCS) affect the early development of marine fish; however, the corresponding molecular mechanisms are still not fully understood. Therefore, this work aims to study the effects of the single and combined exposure to these stressors during the thyroid-regulated metamorphosis of the flatfish Solea senegalensis. Sub-lethal exposure (5.89 kJ m^-2 UV and/or 0.546 and 1.090 mg L^-1 TCS for 48 h) was performed at the beginning of metamorphosis (13 days after hatching, dah), followed by a period in clean media until complete metamorphosis (24 dah). Malformations, metamorphosis progression, length, behavior and the expression of thyroid axis-related genes were studied. TCS induced malformations, decreased swimming performance, and induced metamorphosis acceleration at 15 dah, followed by a significant metamorphosis delay. Such effects were more noticeable in the presence of UV. The down-regulation of five thyroid axis-related genes occurred after exposure to TCS (15 dah), and after 9 days in clean media two genes were still down-regulated. UV exposure increased the effect of TCS by further down-regulating gene expression immediately after the exposure. Since several effects persisted after the period in clean media, implications of these stressors (mainly TCS) on the ecological performance of the species are suggested.

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.