Iodine and thyroid hormones – modelling moderate iodine deficiency with sodium perchlorate in mice

Introduction

Iodine is an essential trace element for thyroid hormone (TH) production. In adults, THs play important roles in almost all organ systems including heart, lungs, skeletal muscles and metabolism. Iodine is taken in by ingestion and its intake is decreasing in many countries leading to mild iodine deficiency especially in Europe. Several mouse models exist for a severe iodine deficiency that leads to a decrease in TH levels but not many studies have addressed mild iodine deficiency.

Materials and methods

We studied the possibility to create a mouse model for moderate iodine deficiency with exposure to sodium perchlorate, which blocks iodine transport to thyrocytes. Two doses of perchlorate, 1 and 5 μg/mL, were administered via drinking water to male and female 2-month-old C57BL/6 J mice for 5 weeks and circulating TH and iodine levels were measured. Body weight and fluid consumption were analysed throughout the exposure.

Results and discussion

Thyroid morphology and follicle size were analysed in the end of the exposure. The high dose animals had increased liquid consumption, their thyroid morphology was severely damaged, they displayed a decrease in circulating thyroxine levels and their circulating iodine levels were decreased in both sexes. The low dose animals displayed decreased thyroid follicle size but without a decrease in circulating T4 levels except for females after 5 weeks of exposure. In the low dose animals, the circulating iodine levels did not decrease but a tendency to diminished iodine levels was observed in females. We could thus show differential responses to perchlorate exposure between sexes and propose the low dose, 1 μg/mL, of perchlorate as a model for moderate iodine deficiency.

Conclusion

Moderate iodine deficiency, especially during pregnancy when the needs double, could make individuals more vulnerable to environmental pollution targeting TH signalling.