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Protective effect of KI in mtDNA in porcine thyroid: comparison with KIO₃ and nDNA.

Karbownik-Lewinska M, Stepniak J, Milczarek M, Lewinski A - Eur J Nutr (2014)

Bottom Line: 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 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Oncological Endocrinology, Medical University of Lodz, 7/9 Zeligowski St., 90-752, Lodz, Poland, MKarbownik@hotmail.com.

ABSTRACT

Purpose: 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.

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Oxidative damage to nuclear DNA in porcine thyroid. nDNA was incubated in the presence of KI or KIO3 [50; 25; 10; 5.0; 2.5 mM] alone or together with Fenton reaction substrates, i.e., FeSO4 [30 μM] plus H2O2 [0.5 mM]. Data are expressed as the ratio 8-oxodG/dG × 105. Data are from three independent experiments. Values are expressed as mean ± SE (error bars). ap < 0.05 vs. control; bp < 0.05 vs. Fe2++H2O2 (in the absence of KI or KIO3); *p < 0.05 vs. respective concentration of KI or KIO3 alone (i.e., in the absence of Fe2++H2O2). Statistical evaluation was performed separately for KI (white bars) and for KIO3 (black bars)
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Fig1: Oxidative damage to nuclear DNA in porcine thyroid. nDNA was incubated in the presence of KI or KIO3 [50; 25; 10; 5.0; 2.5 mM] alone or together with Fenton reaction substrates, i.e., FeSO4 [30 μM] plus H2O2 [0.5 mM]. Data are expressed as the ratio 8-oxodG/dG × 105. Data are from three independent experiments. Values are expressed as mean ± SE (error bars). ap < 0.05 vs. control; bp < 0.05 vs. Fe2++H2O2 (in the absence of KI or KIO3); *p < 0.05 vs. respective concentration of KI or KIO3 alone (i.e., in the absence of Fe2++H2O2). Statistical evaluation was performed separately for KI (white bars) and for KIO3 (black bars)

Mentions: Under basal conditions, two examined substances, i.e., KI and KIO3, did reveal similar effects, but in the presence of Fenton reaction substrates, effects of KI and KIO3 on oxidative damage to nDNA and to mtDNA isolated from porcine thyroid tissue differed substantially. Neither KI nor KIO3 did increase the level of oxidative damage to nDNA (Fig. 1).Fig. 1


Protective effect of KI in mtDNA in porcine thyroid: comparison with KIO₃ and nDNA.

Karbownik-Lewinska M, Stepniak J, Milczarek M, Lewinski A - Eur J Nutr (2014)

Oxidative damage to nuclear DNA in porcine thyroid. nDNA was incubated in the presence of KI or KIO3 [50; 25; 10; 5.0; 2.5 mM] alone or together with Fenton reaction substrates, i.e., FeSO4 [30 μM] plus H2O2 [0.5 mM]. Data are expressed as the ratio 8-oxodG/dG × 105. Data are from three independent experiments. Values are expressed as mean ± SE (error bars). ap < 0.05 vs. control; bp < 0.05 vs. Fe2++H2O2 (in the absence of KI or KIO3); *p < 0.05 vs. respective concentration of KI or KIO3 alone (i.e., in the absence of Fe2++H2O2). Statistical evaluation was performed separately for KI (white bars) and for KIO3 (black bars)
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4323512&req=5

Fig1: Oxidative damage to nuclear DNA in porcine thyroid. nDNA was incubated in the presence of KI or KIO3 [50; 25; 10; 5.0; 2.5 mM] alone or together with Fenton reaction substrates, i.e., FeSO4 [30 μM] plus H2O2 [0.5 mM]. Data are expressed as the ratio 8-oxodG/dG × 105. Data are from three independent experiments. Values are expressed as mean ± SE (error bars). ap < 0.05 vs. control; bp < 0.05 vs. Fe2++H2O2 (in the absence of KI or KIO3); *p < 0.05 vs. respective concentration of KI or KIO3 alone (i.e., in the absence of Fe2++H2O2). Statistical evaluation was performed separately for KI (white bars) and for KIO3 (black bars)
Mentions: Under basal conditions, two examined substances, i.e., KI and KIO3, did reveal similar effects, but in the presence of Fenton reaction substrates, effects of KI and KIO3 on oxidative damage to nDNA and to mtDNA isolated from porcine thyroid tissue differed substantially. Neither KI nor KIO3 did increase the level of oxidative damage to nDNA (Fig. 1).Fig. 1

Bottom Line: 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 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Oncological Endocrinology, Medical University of Lodz, 7/9 Zeligowski St., 90-752, Lodz, Poland, MKarbownik@hotmail.com.

ABSTRACT

Purpose: 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.

Show MeSH
Related in: MedlinePlus