Identifying a potential role of immune cells in gadolinium deposition within the brain

BACKGROUND: Gadolinium (Gd) deposition in the brain was observed in patients with history of gadolinium-based contrast agent (GBCA) administration. However, the exact mechanism behind this deposition remains unclear, especially given that an intact blood-brain barrier (BBB) is considered impermeable to GBCA. In this study, we propose that immune cells might play a role in facilitating GBCA entry into the brain despite an intact BBB. METHODS: Gadoterate meglumine, gadoteridol, gadobutrol and gadodiamide were investigated as GBCAs. Immune cells from human donor buffy coats were isolated, incubated with the GBCA and used in the experiments. Gd associated with the immune cells were measured using single-cell inductively coupled mass spectrometry (SC-ICP-MS). Flow cytometry analysis was performed to characterise the adhesion molecule expression profile on the immune cells and binding assay was employed to check the binding of Gd treated immune cells with endothelial ligands in static conditions. An in vitro model of the human BBB that prevents free diffusion of GBCA across was further used to observe immune cell behaviour at the BBB under physiological flow, in vitro. RESULTS: Our findings confirm that various immune cells, including CD4+ T cells, CD8+ T cells, monocytes, NK cells and B cells are capable of taking up the different GBCAs. Furthermore, we demonstrate that GBCA loading does not impair immune cell interaction with the endothelial ligands required for successful extravasation across the BBB under static conditions. Most importantly, we show that T cells and monocytes, loaded with the different contrast agents, extravasated across an in vitro BBB model under physiological flow conditions in a comparable manner to non GBCA loaded cells. CONCLUSIONS: Taken together, our in vitro observations show that immune cells can transport GBCA across the BBB and could lead to permanent deposition of Gd in the brain.