Abstract
Heavy metals are essential for a wide range of biological processes, including the growth and reproduction of cells, synthesis of biomolecules, many enzymatic reactions, and the body’s immunity, but their excessive intake is harmful. Specifically, they cause oxidative stress (OS) and generate free radicals and reactive oxygen species (ROS) in metabolism. In addition, the accumulation of heavy metals in humans can cause serious damage to different organs, especially respiratory, nervous and reproductive and digestive systems. Biologically, metal chelation therapy is often used to treat metal toxicity. This process occurs through the interaction between the ligand and a central metal atom, forming a complex ring-like structure. After metals are chelated with appropriate chelating agents, their damage in metabolism can be prevented and efficiently removed from the body. On the other hand, heavy metals, including Zn, Fe and Cu, are necessary for the suitable functioning of different proteins including enzymes in metabolism. However, when the same metals accumulate at levels higher than the optimum level, they can easily become toxic and have harmful effects toward biomolecules. In this case, it induces the formation of ROS and nitrogen species (RNS) resulting in peroxidation of biological molecules such as lipids in the plasma membrane. Antioxidants have an increasing interest in many fields due to their protective effects, especially in food and pharmaceutical products. Screening of antioxidant properties of compounds needs appropriate methods including metal chelating assay. In this study, a general approach to the bonding and chelating properties of metals is described. For this purpose, the basic principles and chemical principles of metal chelation methods, both in vivo and in vitro, are outlined and discussed. Hence, in the main sections of this review, the descriptions related to metal ions, metal chelating, antioxidants, importance of metal chelating in biological system and definitions of metal chelating assays as widely used methods to determine antioxidant ability of compounds are provided. In addition, some chemical properties, technical and critical details of the used chelation methods are given.
Highlights
Heavy MetalsMetal ions are necessary for the continuation of the vital functions of living organisms
Iron overloads can be decreased by the management of agents that can compete with the transferrin protein, which binds and transfers metal ions
It has been reported that the main antioxidant ability of resveratrol, a strong and natural antioxidant, may be related to its iron binding capacity
Summary
Metal ions are necessary for the continuation of the vital functions of living organisms. Iron overloads can be decreased by the management of agents that can compete with the transferrin protein, which binds and transfers metal ions. Al toxicity induces an excessive increase in ROS levels It promotes different neurodegenerative diseases including dementia and encephalopathy in humans. This toxicity causes serious damage to biomolecules. The presence of Al in living systems creates different toxic effects Another effect is the change in the natural structure and roles of proteins and enzymes in the glycolysis and TCA pathways, cells, tissues, central nervous system (CNS), and other organs [21]. Al as a strong Lewis acid prefers oxygen donor ligands, including phosphates, nucleotides, carboxylates and nucleic acids Murexide is used in analytical chemistry for complexometric titrations, most often as a complexometric indicator for Ca2+ ions, and for Co2+ , Cu2+ , Ni2+ , Cd2+ , Zn2+ and Pb2+ and rare earth metals [26]
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