EPR-based Assessment of Gadolinium-based Contrast Agent Retention and Gadolinium Transchelation in Inflamed Murine Brain.

objectivesIn view of the mounting evidence for markedly increased cerebellar Gd retention under neuroinflammatory conditions after repeated linear GBCA administration in vivo , we aimed to discriminate between Gd retained within the GBCA complex and forms dissociated from the complex within the CNS and to characterize the chemical environment of the released Gd³⁺. For this purpose, we used electron paramagnetic resonance (EPR) spectroscopy, which enables direct detection of Gd³⁺ release and evaluation of its molecular surroundings in intact cerebellar tissue from inflamed and noninflamed brain sections exposed to either linear or macrocyclic GBCAs. MATERIALS AND

methodsWe performed EPR and electron-nuclear double resonance (ENDOR) experiments on sub-mm brain samples taken after administration of linear gadopentetate-dimeglumine and macrocyclic gadobutrol in vivo in a murine multiple sclerosis model and ex vivo in organotypic hippocampal slice cultures under inflammatory conditions. Complementary mass spectrometry (MS) and MRI calibration experiments on Gd-spiked homogenized mouse brain tissue were used to identify potential Gd bindings and assess the relaxation-active fraction of retained Gd.

resultsEPR detected µM range Gd levels in intact cerebellar biopsies and slices and distinguished between complex-bound and released Gd following linear GBCA administration in vivo . In biopsies, we detected by ENDOR phosphorus-containing molecules in the microenvironment of released Gd. Binding to inorganic ligands was evidenced using MS and MRI calibration experiments in homogenized mouse brain tissue.

conclusionsEPR and ENDOR proved to be sensitive methods for detecting Gd³⁺ release and characterizing retained Gd species within intact brain tissue. Our findings demonstrate inflammation-promoted Gd retention, underscore the importance of integrating in vivo and ex vivo analyses to unravel mechanisms of long-term Gd retention, and suggest that conventional MRI may underestimate the true extent of Gd accumulation, especially under neuroinflammatory conditions.