Endocrine Abstracts

Potassium bromate (KBrO₃) is a known prooxidant and carcinogen. Melatonin is a highly effective antioxidant. Indole-3-propionic acid (IPA) – an indole substance, and propylothiouracil (PTU) – an antithyroid drug, also reveal some antioxidative effects. The aim of the study was to evaluate KBrO₃-induced lipid peroxidation in vitro in tissues collected from either control or melatonin-treated rats, and to compare potential preventive effects of melatonin, IPA and PTU.

Kidney, liver and lung homogenates from either the control or the melatonin-treated rats (0.0645 mmol/kg b.w., i.p., twice daily, for 10 days) were incubated in the presence of KBrO₃ (0.1, 0.5, 1.0, 2.5, 5.0, 10.0 mM). As prooxidative effect of KBrO₃ was observed only in the control lung homogenates, they were then incubated in the presence of KBrO₃ (10.0 mM) plus melatonin (0.01, 0.1, 0.5, 1.0, 5.0, 7.5 mM), or IPA or PTU (0.01, 0.1, 0.5, 1.0, 5.0, 7.5, 10.0 mM). The level of lipid peroxidation products – malondialdehyde +4-hydroxyalkenals (MDA+4-HDA) – was measured spectrophotometrically.

KBrO₃ treatment increased lipid peroxidation in the control lung homogenates, but not in the lung from the melatonin-treated rats. Melatonin, IPA and PTU reduced KBrO₃-induced lipid peroxidation. Unexpectedly, KBrO₃ caused a concentration-dependent decrease in lipid peroxidation in liver and kidney homogenates from the control rats, whereas such an effect was less pronounced in tissues from the melatonin-treated rats.

In conclusion, KBrO₃-induced lipid peroxidation in rat lung suggests that it may be the target organ for this carcinogen. An exposure of an organism to melatonin decreases tissue sensitivity to KBrO₃-induced damage, possibly by restoring the oxidative balance. Thus, melatonin could be recommended for its possible cancer prevention effects.