Metal Complexes of Biologically Active Ligands as Potential Antioxidants

Recent years have witnessed an unprecedented progress in biological applications of metal coordination compounds of biologically active ligands because of their key role in clinical therapy. Transition metals are particularly suitable for this purpose because they can adopt a wide variety of coordination numbers, geometries and oxidation states in comparison with other main group elements. One of the characteristics of metals is their potential to undergo redox processes, as determined by their redox potentials. Especially, transition metal ions are usually able to switch between several oxidation states. Due to the redox activity of metals and, therefore, a possible disturbance of the sensitive cellular redox homeostasis, a tight regulation of the metal and redox balance is crucial for health. On the other hand, over production of activated oxygen species, generated by normal metabolic process, is considered to be the main contributor to oxidative damages to biomolecules such as DNA, lipids and proteins, thus accelerating cancer, aging, inflammation, cardiovascular and neurodegenerative diseases. The potential value of antioxidants has already prompted investigators to search for the cooperative effects of metal complexes and natural compounds for improving antioxidant activity. Depending on their structure and on the source of the oxidative stress, metal complexes might act as antioxidants or prooxidants. The current review provides insight into the interaction between the reactive oxygen species and the transition metals and their complexes. It will focus on a novel approach to design synthetic antioxidant metal-based compounds and to study their activities in the oxidation processes. This work underlines some important features for the research on metal complexes of biologically active ligands as antioxidants, and supports future evaluation of some of these compounds as possible therapeutic agents.