Abstract
Background: The alkaloid 8-hydroxyquinoline (8HQ) is well-known for various biological activities, including antioxidant effects and especially for the formation of coordination complexes with various transition metals, such as iron, amongst others. Therefore, 8HQ was extensively explored as a promising antineurodegenerative agent. However, other authors noted pro-oxidant effects of 8HQ. Here, we explore the pro- and antioxidant properties of 8HQ, especially in context of coordination complexes with iron (II) and iron (III). Methods: Nano-electrospray−mass spectrometry, differential pulse voltammetry, deoxyribose degradation, iron (II) autoxidation, and brine shrimp mortality assays were used. Results: 8HQ formed a complex mixture of coordination complexes with iron (II) and iron (III). Furthermore, 8HQ showed antioxidant effects but no pro-oxidant ones. In the brine shrimp mortality assay, 8HQ demonstrated toxicity that decreased in the presence of iron (III). Conclusions: 8HQ is a potent antioxidant whose effects depend not only on the formation of the coordination complexes with iron ions, but surely on the scavenging activities due to the redox properties of the 8-hydroxyl group. No pro-oxidant effects were observed in the set of the used assays.
Highlights
The alkaloid 8-hydroxyquinoline (8HQ) is well-known for various biological activities, including antioxidant effects and especially for the formation of coordination complexes with various transition metals, such as iron, amongst others
The curative effects of 8HQ depend primarily on direct scavenging and on its ability to form coordination complexes with transition metals such as iron [10]. These metals can accumulate in the brain tissue under pathological conditions, and can accelerate tissue destruction by catalyzing the formation of cytotoxic reactive oxygen species (ROS), especially hydroxyl radicals [11]
The toxicity of 8HQ and its coordination complexes with iron was studied by examining its effects on brine shrimp mortality—an assay that is commonly used for screening biological activities [20]
Summary
8-Hydroxyquinoline (oxine, 8-quinolinol, 8HQ) is an alkaloid with a rather simple chemical structure and occurs in plants of families Asteraceae [1] and Euphorbiaceae [2]. The curative effects of 8HQ depend primarily on direct scavenging and on its ability to form coordination complexes with transition metals such as iron [10] These metals can accumulate in the brain tissue under pathological conditions, and can accelerate tissue destruction by catalyzing the formation of cytotoxic reactive oxygen species (ROS), especially hydroxyl radicals [11]. We explored the coordination complex formation ability of 8-hydroxyquinoline with iron, their pro- and antioxidant properties, and their toxic effects For this purpose, we used nano-ESI−MS and a set of well-established assays: deoxyribose degradation [17], metal autoxidation [18], and brine shrimp (Artemia salina L.) mortality [19,20]. The toxicity of 8HQ and its coordination complexes with iron was studied by examining its effects on brine shrimp mortality—an assay that is commonly used for screening biological activities [20]
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