Subcutaneous deuterated substrate administration in mice: An alternative to tail vein infusion

Purpose: Tail-vein catheterization and subsequent in-magnet infusion is a common route of administration of deuterium (²H)-labeled substrates in small-animal deuterium (D) MR studies. With mice, because of the tail vein's small diameter, this procedure is challenging. It requires considerable personnel training and practice, is prone to failure, and may preclude serial studies. Motivated by the need for an alternative, the time courses for common small-molecule deuterated substrates and downstream metabolites in brain following subcutaneous infusion were determined in mice and are presented herein. Methods: Three ²H-labeled substrates—[6,6-²H₂]glucose, [²H₃]acetate, and [3,4,4,4-²H₄]beta-hydroxybutyrate—and ²H₂O were administered to mice in-magnet via subcutaneous catheter. Brain time courses of the substrates and downstream metabolites (and semi-heavy water) were determined via single-voxel DMRS. Results: Subcutaneous catheter placement and substrate administration was readily accomplished with limited personnel training. Substrates reached pseudo-steady state in brain within ∼30–40 min of bolus infusion. Time constants characterizing the appearance in brain of deuterated substrates or semi-heavy water following ²H₂O administration were similar (∼15 min). Conclusion: Administration of deuterated substrates via subcutaneous catheter for in vivo DMRS experiments with mice is robust, requires limited personnel training, and enables substantial dosing. It is suitable for metabolic studies where pseudo-steady state substrate administration/accumulation is sufficient. It is particularly advantageous for serial longitudinal studies over an extended period because it avoids inevitable damage to the tail vein following multiple catheterizations.