Endocrine Abstracts

Introduction: Fenton reaction (Fe²⁺+H₂O₂ →Fe³⁺+ ′OH+OH⁻) is of special significance in the thyroid gland, as both its substrates, i.e. H₂O₂ and Fe²⁺, are required for thyroid hormone synthesis. Also iodine, an essential element supplied by the diet, is indispensable for thyroid hormone synthesis. It is well known that iodine affects red-ox balance. One of the most frequently examined oxidative processes is lipid peroxidation (LPO), which results from oxidative damage to membrane lipids.

The aim of the study was to evaluate effects of iodine, used as potassium iodide (KI) or potassium iodate (KIO₃), on LPO in porcine thyroid homogenates under basal conditions and in the presence of Fenton reaction substrates.

Methods: Porcine thyroid homogenates were incubated in the presence of KI (0.00005–500 mM) or KIO₃ (0.00005–200 mM), without or with addition of FeSO₄ (30 μM) +H₂O₂ (0.5 mM). Concentration of malondialdehyde+4-hydroxyalkenals (MDA+4-HDA) was measured spectrophotometrically, as an index of LPO.

Results: Potassium iodide, used in the lowest concentrations (≤0.05 mM), did not affect LPO; KI in concentrations of 0.1–1.0 mM, resulting in thyroid level of inorganic iodine close to that observed under normal iodine supply, clearly decreased the basal LPO; in the highest concentrations of 10–500 mM, KI increased LPO. At the same time, KI used in the middle range of concentrations (10–50 mM) reduced Fenton reaction-induced LPO. In opposite, KIO₃ revealed, depending on the concentration, either no protective effect at all or even strong prooxidative action.

Conclusion: Potassium iodide, used in doses generally recommended in iodide prophylaxis, may prevent oxidative damage to membrane lipids in porcine thyroid. Toxic effects of iodide overload may result from its prooxidative action. Potassium iodate does not possess any direct beneficial effects on red-ox balance in the thyroid, which constitutes an additional argument against its utility in iodine prophylaxis.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This work was supported, however funding details unavailable.