Effect of Long Term Excessive Iodine Intake on Thyroid Function and Oxidative Stress in Euthyroid and Hypothyroid Rats

Abstract

Background and aim of work: The aim of the current study was to investigate theeffects of long term excessive iodine intake on gene expression of thyroidal sodiumiodide symporter (NIS), D1 deiodinase and thyroid peroxidase (TPO), thyroidhormones, oxidative injury and anti-oxidative ability of euthyroid and hypothyroidSprague Dawley rats. Materials and Methods: Ninety rats were divided intoeuthyroid and hypothyroid (thiocyanate induced) groups with or withoutadministration of excess iodine (3000 or 6000 μg/l) for 4 weeks. Serum thyroxine (T4),triiodothyronine (T3), TSH, thyroid antioxidants ((glutathione S transferase, catalase,superoxide dismutase enzymes, nitric oxide and total antioxidants), lipid peroxide(malondialdehyde, MDA) were measured. RT-PCR gene expression for thyroidal NIS,D1 deiodinase and TPO were performed. Results: Thiocyanate significantlydecreased thyroid hormones (T3, T4), increased lipid peroxides and antioxidants,increased gene expression of NIS, D1 deiodinase, TPO. High iodine intake tohypothyroid rats significantly decreased NIS, D1 deiodinase and TPO genesexpression. Excess iodine significantly increased MDA and antioxidants in euthyroidand hypothyroid rats. Despite the increase in T4 in euthyroid rats administered excessiodine, T3 decreased whereas in hypothyroid rats, both of them were increased. NIS,and D1 deiodinase genes expression in euthyroid rats administered excess iodinewere decreased but TPO was non-significantly increased. Conclusion:Hypothyroidism increased gene expression of NIS, TPO, and induces an oxidativestress. High iodine intake decreased NIS and D1 deiodinase gene expression ineuthyroid and hypothyroid rats. Moreover, excess iodine increase thyroid hormones,lipid peroxides and antioxidants in cases of euthyroid and hypothyroid rats.Therefore, screening of thyroid function and assessment of prooxidant/antioxidantstatus in subjects treated with drugs containing iodine and after investigations withcontrast media are recommended.