Melatonin reduces high levels of lipid peroxidation induced by potassium iodate in porcine thyroid

Abstract

Abstract. Iodine is essential for thyroid hormone synthesis. Under normal iodine supply, calculated physiological iodine concentration in the thyroid is approx. 9 mM. Either potassium iodide (KI) or potassium iodate (KIO3) are used in iodine prophylaxis. KI is confirmed as absolutely safe. KIO3 possesses chemical properties suggesting its potential toxicity. Melatonin (N-acetyl-5-methoxytryptamine) is an effective antioxidant and free radical scavenger. Study aims: to evaluate potential protective effects of melatonin against oxidative damage to membrane lipids (lipid peroxidation, LPO) induced by KI or KIO3 in porcine thyroid. Homogenates of twenty four (24) thyroids were incubated in presence of either KI or KIO3 without/with melatonin (5 mM). As melatonin was not effective against KI-induced LPO, in the next step only KIO3 was used. Homogenates were incubated in presence of KIO3 (200; 100; 50; 25; 20; 15; 10; 7.5; 5.0; 2.5; 1.25 mM) without/with melatonin or 17ß-estradiol. Five experiments were performed with different concentrations of melatonin (5.0; 2.5; 1.25; 1.0; 0.625 mM) and one with 17ß-estradiol (1.0 mM). Malondialdehyde + 4-hydroxyalkenals (MDA + 4-HDA) concentration (LPO index) was measured spectrophotometrically. KIO3 increased LPO with the strongest damaging effect (MDA + 4-HDA level: ≈1.28 nmol/mg protein, p < 0.05) revealed at concentrations of around 15 mM, thus corresponding to physiological iodine concentrations in the thyroid. Melatonin reduced LPO (MDA + 4-HDA levels: from ≈0.97 to ≈0,76 and from ≈0,64 to ≈0,49 nmol/mg protein, p < 0.05) induced by KIO3 at concentrations of 10 mM or 7.5 mM. Conclusion: Melatonin can reduce very strong oxidative damage to membrane lipids caused by KIO3 used in doses resulting in physiological iodine concentrations in the thyroid.

Cumulative Protective Effect of Melatonin and Indole-3-Propionic Acid against KIO3—Induced Lipid Peroxidation in Porcine Thyroid

“…In the Experiment I, IPA (10 mM) and melatonin (5 mM), applied separately, reduced KIO 3 -induced lipid peroxidation when this prooxidant was used at concentrations of 10 mM, 7.5 mM or 5.0 mM (Figure 1), which is in line with the results of our previous studies [14,15]. However, in Experiment II with the use of additional concentrations of KIO 3 , IPA revealed protective effects against higher concentration of KIO 3 (16.25 mM) than melatonin did (KIO in the concentration of 15 mM) (Figure 2).…”

“…In the Experiment I, IPA (10 mM) and melatonin (5 mM), applied separately, reduced KIO 3 -induced lipid peroxidation when this prooxidant was used at concentrations of 10 mM, 7.5 mM or 5.0 mM ( Figure 1 ), which is in line with the results of our previous studies [ 14 , 15 ].…”

“…The concentrations of KIO 3 [ 12 , 14 , 15 ], of melatonin and of IPA [ 14 , 15 , 33 , 38 ] were chosen on the basis of the results of our previous studies; the highest achievable concentrations of melatonin and IPA resulting from their limited solubility were used.…”

“…KIO 3 , in contrast to KI, is the oxidant and thereby may react easily with oxidizable substances [11]. It has been documented recently that KIO 3 and KI reveal different in vitro effects on oxidative damage to macromolecules in the thyroid [12][13][14][15]. In these studies, KIO 3 did not reveal any protective effects; instead, it damaged by itself membrane lipids with the strongest damaging effect observed at concentrations of 10 mM [12] or of 15 mM [14,15], which both correspond to physiological iodine concentration in the thyroid [16][17][18].…”

“…In our previous studies we have observed that not only melatonin [ 14 ], but also IPA [ 15 ] are able—in concentration-dependent manner—to reduce oxidative damage to membrane lipids caused by KIO 3 , when this compound was used in doses close to physiological iodine concentrations in the thyroid. In the present study we decided to check if melatonin used together with IPA (in their highest achievable in vitro concentrations resulting from their limited solubility) reveals stronger protective effects against KIO 3 -induced oxidative damage to membrane lipids in porcine thyroid homogenates comparing to protective effects of each antioxidant used separately.…”