Pro-Oxidative Effect of KIO3 and Protective Effect of Melatonin in the Thyroid—Comparison to Other Tissues

Abstract

Not only iodine deficiency, but also its excess may contribute to thyroid cancer. Potassium iodate (KIO3), which is broadly used in the salt iodization program, can increase oxidative damage to membrane lipids (lipid peroxidation, LPO) under experimental conditions, with the strongest damaging effect at KIO3 concentration of ~10 mM (corresponding to physiological iodine concentration in the thyroid). Melatonin is an effective antioxidant, which protects against KIO3-induced LPO in the thyroid. This study aimed to compare the protective effects of melatonin, used in the highest achievable in vitro concentration, against KIO3-induced oxidative damage to membrane lipids in various porcine tissues (thyroid, ovary, liver, kidney, brain, spleen, and small intestine). Homogenates were incubated in the presence of KIO3 (20; 15; 10; 7.5; 5.0; 0.0 mM) without/with melatonin (5 mM). The malondialdehyde + 4-hydroxyalkenals (MDA + 4-HDA) concentration (LPO index) was measured spectrophotometrically. KIO3 increased the LPO in all examined tissues; in the thyroid, the damaging effect of KIO3 (10; and 7.5 mM) was lower than in other tissues and was not observed for the lowest concentration of 5 mM. Melatonin reduced LPO induced by KIO3 (10, 7.5, and 5 mM) in all tissues, and in the thyroid it was also protective against as high a concentration of KIO3 as 15 mM; the LPO level resulting from KIO3 + melatonin treatment was lower in the thyroid than in other tissues. In conclusion, the thyroid is less sensitive tothe pro-oxidative effects of KIO3 compared to other tissues. The strongest protective effect of melatonin was observed in the thyroid, but beneficial effects were significant also in other tissues. Melatonin should be considered to avoid the potential damaging effects of iodine compounds applied in iodine prophylaxis.

Membrane Lipids in the Thyroid Comparing to Those in Non-Endocrine Tissues Are Less Sensitive to Pro-Oxidative Effects of Fenton Reaction Substrates

“…Our study is probably the first attempt to compare the damaging effects of high iron concentrations in the thyroid and in various nonendocrine tissues under in vitro conditions. It should be stressed that the lower sensitivity of thyroidal membrane lipids, compared to that of membrane lipids in non-endocrine tissues, in response to high iron concentrations, is similar to previously observed pro-oxidative effects of KIO 3 (Iwan et al, 2021a). Therefore, we suppose that membrane lipids (and possibly other biological macromolecules) in the thyroid reveal higher resistance to any external pro-oxidative agent than those in other tissues.…”

“…One of the most famous antioxidants is melatonin (N-acetyl-5-methoxytryptamine), which is produced in the organism mostly by the pineal gland, but it is also available as an exogenous substance. This molecule is confirmed to be a very effective antioxidant and free radical scavenger which prevents oxidative damage not only in the thyroid (Lewinski and Karbownik, 2002;Karbownik et al, 2005;Kokoszko-Bilska et al, 2014;Zasada and Karbownik-Lewinska, 2015;Iwan et al, 2021aIwan et al, , 2021bStepniak et al, 2021) but also in many other tissues and organs (Karbownik et al, 2000(Karbownik et al, , 2001a(Karbownik et al, , 2001b(Karbownik et al, , 2006Gitto et al, 2001;Osuna et al, 2002;Mogulkoc et al, 2006;Reiter et al, 2017). In the current study, we have observed that melatonin reduced LPO induced by Fenton reaction substrates in all examined tissues, and this protective effect was independent of iron concentration.…”

“…Under basal conditions, these thyroid systems effectively fulfill their antioxidant role. In our both studies (the present and the previous by Iwan et al, 2021a), we have observed that the basal level of LPO in the thyroid gland is not higher than that in other tissues. However, under any pathological condition associated either with endogenous abnormalities or exposure to exogenous pro-oxidants, this redox balance may be disrupted and, in consequence, the level of oxidative damage can be increased, resulting in various diseases (Valko et al, 2007), such as cancer (Ziech et al, 2011).…”

“…In our earlier studies, we have observed that the thyroid gland is less sensitive to the damaging effects of iron than the ovary which is also an endocrine gland (Rynkowska et al, 2020). We have also evaluated the damaging effect of KIO 3 and have found that KIO 3induced LPO is significantly lower in the thyroidal tissue than non-endocrine tissues and the ovary (Iwan et al, 2021a). Our present results confirm the results cited previously and clearly indicate that membrane lipids in the thyroid are less sensitive to pro-oxidative events occurring in this gland.…”

Correction: Iwan et al. Pro-Oxidative Effect of KIO3 and Protective Effect of Melatonin in the Thyroid—Comparison to Other Tissues. Life 2021, 11, 592

“…In the original article [ 1 ], there was a mistake in Figure 2 as published, namely the graph showing the levels of lipid peroxidation in the ovary was inserted twice and, at the same time, the graph showing the levels of lipid peroxidation in the spleen was not inserted at all. The corrected Figure 2 appears below.…”