Comparison of potential protective effects of melatonin, indole‐3‐propionic acid, and propylthiouracil against lipid peroxidation caused by potassium bromate in the thyroid gland

Abstract

Potassium bromate (KBrO3) is a prooxidant and carcinogen, inducing thyroid tumors. Melatonin and indole-3-propionic acid (IPA) are effective antioxidants. Some antioxidative effects of propylthiouracil (PTU)--a thyrostatic drug--have been found. The aim of the study was to compare protective effects of melatonin, IPA, and PTU against lipid peroxidation in the thyroids, collected from rats treated with KBrO3, and in homogenates of porcine thyroids, incubated in the presence of KBrO3. Wistar rats were administered KBrO3 (110 mg/kg b.w., i.p., on the 10th day of the experiment) and/or melatonin, or IPA (0.0645 mmol/kg b.w., i.p., twice daily, for 10 days), or PTU (0.025% solution in drinking water, for 10 days). Homogenates of porcine thyroids were incubated for 30 min in the presence of KBrO3 (5 mM) plus one of the antioxidants: melatonin (0.01, 0.1, 0.5, 1.0, 5.0, 7.5 mM), or IPA (0.01, 0.1, 0.5, 1.0, 5.0, 7.5, 10.0 mM), or PTU (0.01, 0.1, 0.5, 1.0, 5.0, 7.5, 10.0 mM). The level of lipid peroxidation products (MDA + 4-HDA) was measured spectrophotometrically in thyroid homogenates. In vivo pretreatment with either melatonin or with IPA or with PTU decreased lipid peroxidation caused by KBrO3--injections in rat thyroid gland. Under in vitro conditions, PTU (5.0, 7.5, and 10.0 mM), but neither melatonin nor IPA, reduced KBrO3-related lipid peroxidation in the homogenates of porcine thyroids. In conclusion, melatonin and IPA may be of great value as protective agents under conditions of exposure to KBrO3.

Protective antioxidative effects of caffeic acid phenethyl ester (CAPE) in the thyroid and the liver are similar to those caused by melatonin

“…It is well known (from many in vivo and in vitro studies) that melatonin is a perfect antioxidant because of its effective protective action against damaging effects of different prooxidants and the fact that under basal conditions it does not change the level of oxidative damage to macromolecules [12,13,31,32]. The observation – made by us in the present study – of the decreasing effect of CAPE on the basal LPO level, was unexpected and also undesirable.…”

Protective effects of melatonin and N‐acetylserotonin on aflatoxin B1‐induced lipid peroxidation in rats

“…35 Co-treatment with Mel prevented the KBrO 3 -induced oxidative damage to lipids in rat kidney and in blood serum, 36 as well as in rat thyroid gland. 37 Pretreatment with Mel likewise reduced indomethacin-induced gastric damage and plasma malondialdehyde level in rats. 38 The protective effects of Mel, observed both in our study and in the studies cited above, could have been due to its ability to scavenge numerous toxic species, such as hydroxyl radical ( OH), peroxynitrite anion (ONOO À ) or nitric oxide (NO ).…”

Recent Developments of Melatonin Related Antioxidant Compounds

“…IPA acts as an endogenous electron donor primarily by detoxifying reactive oxygen species. This mechanism could be responsible for the high efficacy of antioxidative action of IPA in vivo like MLT [82]. It was found that indole derivatives that do not contain the redox active hydroxyl group at position 5 of the indole ring do not act as chain breaking antioxidants and therefore are either poorly protective or not effective in vitro.…”