Quantifying the Transchelation of Gd3+ Ions from Linear and Macrocyclic GBCA to Glycosaminoglycans using MR Relaxometry

In this study, we quantified the dissociation of GBCAs at different ZnCl₂ concentrations and the subsequent chelation of Gd³⁺ to glycosaminoglycans (GAGs) like heparin. We showed that the relaxivity of the resulting Gd-GAG complexes is about seven times higher compared to that of GBCAs. Under physiological conditions, we further showed that ~20% of the Gd³⁺-ions transchelated from linear GBCAs to heparin and that these are accountable for more than 50% of the observed relaxation rate. Therefore, Gd-GAG complexes should be considered as the Gd-containing macromolecular substances with high relaxivity that are needed to explain the observed long-term enhancements in vivo.