Protective effect of KI in mtDNA in porcine thyroid: comparison with KIO₃ and nDNA.
OBJECTIVE
Iodine, bivalent iron (Fe²⁺), and hydrogen peroxide (H₂O₂), all significantly affecting the red-ox balance, are required for thyroid hormone synthesis. Intracellular iodine excess (≥10⁻³ M) transiently blocks thyroid hormonogenesis (an adaptive mechanism called Wolff-Chaikoff effect). The aim of the study was to evaluate the effects of iodine, used as potassium iodide (KI) or potassium iodate (KIO₃), in concentrations corresponding to those typical for Wolff-Chaikoff effect, on the level of oxidative damage to nuclear DNA (nDNA) and mitochondrial DNA (mtDNA) isolated from porcine thyroid under basal conditions and in the presence of Fenton reaction (Fe²⁺+H₂O₂ → Fe³⁺+(·)OH + OH⁻) substrates.


METHODS
Thyroid nDNA and mtDNA were incubated in the presence of either KI or KIO₃ (2.5-50 mM), without/with FeSO₄ (30 µM) + H₂O₂ (0.5 mM). Index of DNA damage, i.e., 8-oxo-7,8-dihydro-2'-deoxyguanosine, was measured by HPLC.


RESULTS
Neither KI nor KIO₃ increased the basal level of 8-oxodG in both nDNA and mtDNA. KI-in all used concentrations-completely prevented the damaging effect of Fenton reaction substrates in mtDNA, and it partially prevented this damage in nDNA. KIO₃ partially prevented Fe²⁺+H₂O₂-induced oxidative damage in both DNA only in its highest used concentrations (≥25 mM).


CONCLUSIONS
Without additional prooxidative abuse, both iodine compounds, i.e., KI and KIO₃, seem to be safe in terms of their potential oxidative damage to DNA in the thyroid. The superiority of KI over KIO₃ relies on its stronger protective effects against oxidative damage to mtDNA, which constitutes an argument for its preferential utility in iodine prophylaxis.
Department of Oncological Endocrinology, Medical University of Lodz, 7/9 Zeligowski St., 90-752, Lodz, Poland, MKarbownik@hotmail.com.
Malgorzata
M
Karbownik-Lewinska
Jan
J
Stepniak
Magdalena
M
Milczarek
Andrzej
A
Lewinski
D000080242:8-Hydroxy-2'-Deoxyguanosine; D000003:Abattoirs; D000818:Animals; D004247:DNA / Q000737:chemistry / Q000187:drug effects / Q000302:isolation & purification; D004249:DNA Damage; D004272:DNA, Mitochondrial / Q000737:chemistry* / Q000187:drug effects / Q000302:isolation & purification; D003849:Deoxyguanosine / Q000031:analogs & derivatives / Q000032:analysis; D019587:Dietary Supplements / Q000009:adverse effects; D005527:Food, Fortified; D006861:Hydrogen Peroxide / Q000037:antagonists & inhibitors / Q000633:toxicity; D007452:Iodates / Q000009:adverse effects / Q000737:chemistry; D007501:Iron / Q000633:toxicity; D009994:Osmolar Concentration; D016877:Oxidants / Q000037:antagonists & inhibitors* / Q000633:toxicity; D010084:Oxidation-Reduction; D017680:Potassium Compounds / Q000009:adverse effects / Q000737:chemistry; D011193:Potassium Iodide / Q000009:adverse effects / Q000737:chemistry*; D020011:Protective Agents / Q000009:adverse effects / Q000737:chemistry*; D034421:Sus scrofa; D013961:Thyroid Gland / Q000737:chemistry
D004272:DNA, Mitochondrial; C045076:Fenton's reagent; D007452:Iodates; D016877:Oxidants; D017680:Potassium Compounds; D020011:Protective Agents; D011193:Potassium Iodide; D000080242:8-Hydroxy-2'-Deoxyguanosine; D004247:DNA; D006861:Hydrogen Peroxide; D007501:Iron; D003849:Deoxyguanosine; C039693:potassium iodate