Comprehensive Speciation Analysis of Residual Gadolinium in Deep Cerebellar Nuclei in Rats Repeatedly Administered With Gadoterate Meglumine or Gadodiamide

Abstract

Purpose: Several preclinical studies have reported the presence of gadolinium (Gd) in different chemical forms in the brain, depending on the class (macrocyclic versus linear) of Gd-based contrast agent (GBCA) administered. The aim of this study was to identify, with a special focus on insoluble species, the speciation of Gd retained in the deep cerebellar nuclei (DCN) of rats administered repeatedly with gadoterate or gadodiamide 4 months after the last injection. Methods: Three groups (N = 6/group) of healthy female Sprague-Dawley rats (SPF/OFA rats; Charles River, L'Arbresle, France) received a cumulated dose of 50 mmol/kg (4 daily intravenous administrations of 2.5 mmol/kg, for 5 weeks, corresponding to 80-fold the usual clinical dose if adjusted for man) of gadoterate meglumine (macrocyclic) or gadodiamide (linear) or isotonic saline for the control group (4 daily intravenous administrations of 5 mL/kg, for 5 weeks). The animals were sacrificed 4 months after the last injection. Deep cerebellar nuclei were dissected and stored at −80°C before sample preparation. To provide enough tissue for sample preparation and further analysis using multiple techniques, DCN from each group of 6 rats were pooled. Gadolinium species were extracted in 2 consecutive steps with water and urea solution. The total Gd concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS). Soluble Gd species were analyzed by size-exclusion chromatography coupled to ICP-MS. The insoluble Gd species were analyzed by single-particle (SP) ICP-MS, nanoscale secondary ion mass spectroscopy (NanoSIMS), and scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy (STEM-EDX) for elemental detection. Results: The Gd concentrations in pooled DCN from animals treated with gadoterate or gadodiamide were 0.25 and 24.3 nmol/g, respectively. For gadoterate, the highest amount of Gd was found in the water-soluble fractions. It was present exclusively as low-molecular-weight compounds, most likely as the intact GBCA form. In the case of gadodiamide, the water-soluble fraction of DCN was composed of high-molecular-weight Gd species of approximately 440 kDa and contained only a tiny amount (less than 1%) of intact gadodiamide. Furthermore, the column recovery calculated for this fraction was incomplete, which suggested presence of labile complexes of dissociated Gd 3+ with endogenous molecules. The highest amount of Gd was detected in the insoluble residue, which was demonstrated, by SP-ICP-MS, to be a particulate form of Gd. Two imaging techniques (NanoSIMS and STEM-EDX) allowed further characterization of these insoluble Gd species. Amorphous, spheroid structures of approximately 100-200 nm of sea urchin-like shape were detected. Furthermore, Gd was consistently colocalized with calcium, oxygen, and phosphorous, strongly suggesting the presence of structures composed of mixed Gd/Ca phosphates. No or occasional colocalization with iron and sulfur was observed. Conclusion: A dedicated analytical workflow pr...

Different Impact of Gadopentetate and Gadobutrol on Inflammation-Promoted Retention and Toxicity of Gadolinium Within the Mouse Brain

“…Using the well-established ABA registration tool, we chose an automated approach to identify T1 relaxation decreases within different brain areas, ensuring higher validity and comparability. The LA-ICP-MS data confirmed the relaxometry findings, as cerebellar Gd levels in EAE mice were 2- to 3-fold higher than in HC mice and within the range previously reported by us and others 15,37,45 . Maximal Gd contents inside the CN and DN after repeated injections of gadopentetate corresponded to approximately 4.51 μg/g in HC mice and 8.28 μg/g in EAE mice (30 μM and 55 μM, respectively).…”

“…In contrast, linear GBCAs at day 24 pfi were present to a large extent in an insoluble form, whereas in its soluble fraction, a portion of Gd was bound to large macromolecules, suggesting that Gd had dissociated from the chelate 15 . These findings were confirmed in recent rodent studies 45,48,49 …”

“…15 These findings were confirmed in recent rodent studies. 45,48,49 We speculate that BBB disruption 37 and/or alterations of the choroid plexus 50 occurring during EAE contribute to the enhanced entry of GBCA into the brain, whereas inflammation-mediated tissue alterations [51][52][53][54] may promote enhanced Gd retention. In healthy individuals, Gd retention inside the brain seems to be the result of an entry of GBCA through the blood-CSF barrier 55 at the choroid plexus and from the CSF via the glymphatic system, 56-59 into the brain.…”

“…The LA-ICP-MS data confirmed the relaxometry findings, as cerebellar Gd levels in EAE mice were 2-to 3-fold higher than in HC mice and within the range previously reported by us and others. 15,37,45 Maximal Gd contents inside the CN and DN after repeated injections of gadopentetate corresponded to approximately 4.51 μg/g in HC mice and 8.28 μg/g in EAE mice (30 μM and 55 μM, respectively).…”

Atomic spectrometry update: review of advances in elemental speciation

“…Continuing on their work into the biomedical fate of Gd-containing MRI contrast agents in the rat brain , the group from Pau in France, have published a third paper 78 in a series investigating the differences between macrocyclic and linear forms of these contrast agents. In this paper they examined the comprehensive speciation analysis of residual Gd in deep cerebellar nuclei (DCN) in rats repeatedly administered either macrocyclic gadoterate meglumine or linear gadodiamide structured GBCAs via 4 daily intravenous administrations of 2.5 mmol kg −1 of drug for 5 weeks, which corresponds to 80-fold the clinical dose if adjusted for patients.…”