Metal Complexes of Omadine (N-Hydroxypyridine-2-thione): Differences of Antioxidant and Pro-Oxidant Behavior in Light and Dark Conditions with Possible Toxicity Implications

Abstract

Omadine or N-hydroxypyridine-2-thione and its metal complexes are widely used in medicine and show bactericidal, fungicidal, anticancer, and photochemical activity. The redox activity of omadine complexes with iron, copper, and zinc on lipid peroxidation under light and dark conditions has been investigated. The monitoring of the oxidation of linoleic acid micelles, resembling a model of lipid membrane, was carried out using nuclear magnetic resonance (1H-NMR). It has been shown that the omadine–zinc complex can induce the oxidation of linoleic acid under light irradiation, whereas the complexes with iron and copper are photochemically stable. All the chelating complexes of omadine appear to be redox-inactive in the presence of hydrogen peroxide under dark conditions. These findings suggest that omadine can demonstrate antioxidant behavior in processes involving reactive oxygen species generation induced by transition metals (Fenton and photo-Fenton reactions). However, the omadine complex with zinc, which is widely used in shampoos and ointments, is photochemically active and may cause oxidative cell membrane damage when exposed to light, with possible implications to health.

Iron Load Toxicity in Medicine: From Molecular and Cellular Aspects to Clinical Implications

“…Vitamin C has iron and other metal-binding capacities and is also a reducing agent, forming a complex with iron (III) followed by reduction to iron (II) [ 266 ]. The biological and clinical activities of iron, ascorbate, and the ascorbate–iron complex can also be affected by many other nutrients and pharmaceutical preparations, which may reduce or potentiate iron toxicity [ 274 , 275 , 276 , 277 , 278 ]. Similar effects to those shown in the interactions of vitamin C and iron are expected from other biomolecules with iron-chelating potential such as folic acid, lipoic acid, and catecholamines, as well as metal ions competing with iron [ 59 , 184 , 185 , 279 , 280 , 281 , 282 , 283 ].…”