Proceedings of The Physiological Society

University of Bristol (2005) J Physiol 567P, PC52

Poster Communications

Iodide excess induces oxidative stress in blood and in thyroid gland

Joanta, Adela Elena; Clichici, Simona; Filip, Adriana; Daicoviciu, Doina;

1. Physiology, University of Medicine and Pharmacy'Iuliu Hatieganu'Cluj-Napoca, Romania, Cluj-Napoca, Romania.

Reactive oxygen species (ROS) play an important role in physiological processes but, when in excess, ROS cause oxidative damage to molecules. Under physiological conditions, the production and detoxification of ROS are more-or-less balanced. Hydrogen peroxide (H2O2) is crucial for thyroid hormone biosynthesis, acting at different steps of the process. Additionally, H2O2 is believed to participate in the Wolff-Chaikoff's effect, in conditions of iodide excess in the thyroid gland. Experiments were performed over 10 days on white, adult, male, Wistar rats, organized in four groups: I, control; II, iodide excess-treated rats (potassium iodide: 1 μg/100g daily in drinking water, corresponding to 400 μg iodide daily intake in human adult); III, iodide excess and selenium-treated rats (0.25 ml/body wt, daily, subcutaneous; 1 ml solution contains 0.5 ml inorganic selenium in stabilized water); and group IV, iodide excess and carbimazole-treated rats (0.1 mg carbimazole/100g, daily, in drinking water). Iodide excess led to an increase in lipid peroxide levels in the thyroid gland (24.81 ± 2.32 μmol malondialdehyde/mg protein) as compared with control (4.98 ± 1.45 μmol malondialdehyde/mg protein) and in serum: (6.46 ± 2.32 nmol malondialdehyde/ml) as compared with control (3.6 ± 1.66 nmol malondialdehyde/ml). Selenium and carbimazole had opposite effects: selenium decreased blood lipid peroxides (4.8 ± 1.98 nmol malondialdehyde/ml) and carbimazole decreased lipid peroxides from both thyroid gland (13.91 ± 1.66 μmol malondialdehyde/mg protein) and serum (5.45 ± 2.33 nmol malondialdehyde/ml). Catalase activity (the amount of hydrogen peroxide (in mg), neutralized by catalase from 0.1 ml protein extract (N cat)) in the thyroid gland increased in selenium-treated animals (20.58 ± 2.88 N cat/mg protein) and decreased under carbimazole administration (5.28 ± 1.67 N cat/mg protein) as compared with iodide-treated animals (11 ± 2.66 N cat/mg protein). Also, superoxiddismutase activity in the thyroid gland increased in iodide excess-treated animals (0.78 ± 0.43 units/mg protein) as compared with control (0.32 ± 0.05 units/mg protein), in selenium-treated animals (1.44 ± 0.66 units/mg protein), and decreased under carbimazole administration (0.06 ± 0.02 units/mg protein). Serum hydrogen donors ability decreased due to iodide excess administration (34.31 ± 3.45% as compared with control, 43.8 ± 2.89%) and increased after selenium (50.14 ± 3.33%) and carbimazole administration (42.34 ± 2.89%). Serum ceruloplasmine level (expressed as mg per % of 100 ml serum) increased in all experimental groups (47.89 ± 2.89 mg % after iodide excess, 67.25 ± 1.89 mg % in selenium-treated animals and 67.37 ± 1.66 mg % after carbimazole administration) as compared with control (16.99 ± 2.44 mg %). Present data suggest that alterations due to iodide excess are mediated through oxidative stress.

Where applicable, experiments conform with Society ethical requirements