Our understanding of metal ions and metal oxide nanoparticles in biological and toxicological oxidative damage contexts continues to evolve.  Determining how biological and dietary antioxidants interact with iron and copper to alter reactive oxygen species (ROS) generation is a fundamental question in this area.  Surprisingly, for example, the stability constants of many sulfur- and selenium-containing amino acids with Fe(II) have not been measured despite their potential importance to the speciation of labile metal ions in the cell.  We have examined the ability of sulfur- and selenium-containing amino acids to bind Cu(II) and Fe(II) using potentiometric titrations, and determined that the presence of S and Se contribute to complex stability for copper much more than iron.  These results suggest that penicillamine, a copper chelator used to treat Wilson’s disease, likely does not alter iron homeostasis by directly coordinating Fe(II).  Metal oxide nanoparticles are known to promote ROS formation, but in many cases the question remains whether damaging ROS are formed at the nanoparticle surface or generated by soluble metal ions dissolved from the nanoparticle.  We determined that CuO nanoparticles produce ROS at the nanoparticle surface and damage DNA differently from dissolved Cu(II) ions.  When combined with CuO nanoparticles, polyphenol compounds show a wide range of activities to both inhibit and promote DNA damage, similar to effects observed for DNA damage caused by copper alone.  Taken together, these studies highlight the potentially dramatic biological effects that small-molecule antioxidants can have when coordinating ROS-generating metal ions or nanoparticles.

From metal ions in solution to metal oxide nanoparticles: An evolving understanding of oxidative damage and antioxidant coordination

ACS Fall 2021

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