7T MRI and molecular studies of Dotarem (gadoterate meglumine) retention in macrophages.

Gadolinium-based MRI contrast agent Dotarem is commonly used in the clinic. Free Gd³⁺ is very toxic. Because the crystallographic radius of Gd³⁺ and Ca²⁺ is very similar, Gd³⁺ can compete with Ca²⁺ in the regulations of cellular functions. Gadolinium is retained in organs and tissues, but the effects of gadolinium retention are mostly unknown. There is also no information how gadolinium retention impacts immune cells and signaling pathways regulated by Ca²⁺ such as RhoA/mTORC1 and mTORC2, which control various, including actin cytoskeleton-dependent, cellular functions. We developed the 7T MRI-based method to analyze gadolinium-based MRI contrast agent retention in isolated immune cells (macrophages) and study the effects of gadolinium retention on the expression of RhoA, mTORC1, mTORC2, and mitochondria, Golgi, and ER markers. We showed that macrophages retain gadolinium for at least seven days after exposure. Gadolinium retention downregulated the expression of RhoA, mTORC1 component Raptor and mTORC2 component Rictor proteins, and dysregulated the expression level of organelle markers. The method described here can be used for monitoring gadolinium levels and effects in isolated cells, such as the immune cells in the blood of patients exposed to contrast-enhanced MRI.