Impact of chelation timing on gadolinium deposition in rats after contrast administration

Objective: To determine if gadolinium (Gd) can be rechelated once released from Gd-based contrast agents (GBCAs) and deposited in vivo. Despite extensive research comparing GBCAs and GBCA formulations as well as the ongoing debate about their risks of deposition and the role of Gd release, it remains unknown if retained Gd can be eliminated by administering chelating agents.

Materials and methods: Rats were injected intravenously with 10 doses of 1 mmol/kg gadodiamide and treated with intravenous Zn-DTPA (30 μmol/kg) concomitantly or 1, 4 or 8 h after GBCA administration (N = 3 rats per group). After euthanization, tissues were harvested three days after the last dose of gadodiamide and tissue Gd concentrations were assessed by ICP-MS. Additionally, a simulation of a single 0.1 mmol/kg gadopentetate dose with 30 μmol/kg DTPA given either concomitantly or within the first 24 h after GBCA was run; simulated tissue Gd concentrations were compared with those observed in rats to determine if simulated trends were accurate.

Results: Concomitant DTPA did not produce a significant reduction in Gd concentration in any organ for rats. There was a time-dependent trend in liver Gd reduction. The 1 h timepoint was associated with a non-significant increase in kidney, brain and femur Gd relative to untreated controls. There were no significant deviations from the model-predicted Gd changes.

Discussion: Both the simulation and rat study did not identify major benefits for chelation at the doses given, despite the simulation assuming all Gd deposited in tissues is unchelated. The potential redistribution in the rat study provide a compelling result that may impact the clinical relevance of further work investigating rechelation of Gd. Future work should further describe the three-dimensional dose-time-response relationship for preventing Gd deposition, and how that relates to long-term Gd toxicities.