Human Serum Albumin Labelled with Sterically-Hindered Nitroxides as Potential MRI Contrast Agents

Molecules. 2020 Apr 8;25(7):1709. doi: 10.3390/molecules25071709.


Four albumin-nitroxide conjugates were prepared and tested as metal-free organic radical contrast agents (ORCAs) for magnetic resonance imaging (MRI). Each human serum albumin (HSA) carrier bears multiple nitroxides conjugated via homocysteine thiolactones. These molecular conjugates retain important physical and biological properties of their HSA component, and the resistance of their nitroxide groups to bioreduction was retained or enhanced. The relaxivities are similar for these four conjugates and are much greater than those of their individual components: the HSA or the small nitroxide molecules. This new family of conjugates has excellent prospects for optimization as ORCAs.

Keywords: homocysteine thiolactone; human serum albumin; magnetic resonance imaging; nitroxide radicals; organic radical contrast agents; spin probes.

MeSH terms

  • Carboxylic Acids / chemistry
  • Cell Death
  • Contrast Media / chemistry*
  • Electron Spin Resonance Spectroscopy
  • Homocysteine / analogs & derivatives
  • Homocysteine / chemistry
  • Humans
  • Kinetics
  • Magnetic Resonance Imaging*
  • Nitrogen Oxides / chemical synthesis
  • Nitrogen Oxides / chemistry*
  • Phantoms, Imaging
  • Protein Structure, Secondary
  • Serum Albumin, Human / chemistry*
  • Staining and Labeling*


  • Carboxylic Acids
  • Contrast Media
  • Nitrogen Oxides
  • Homocysteine
  • homocysteine thiolactone
  • nitroxyl
  • Serum Albumin, Human