Assessment of Metabolic Fluxes in the Mouse Brain in Vivo Using 1H-[13C] NMR Spectroscopy at 14.1 Tesla

Abstract

13C magnetic resonance spectroscopy (MRS) combined with the administration of 13C labeled substrates uniquely allows to measure metabolic fluxes in vivo in the brain of humans and rats. The extension to mouse models may provide exclusive prospect for the investigation of models of human diseases. In the present study, the short-echo-time (TE) full-sensitivity 1H-[13C] MRS sequence combined with high magnetic field (14.1 T) and infusion of [U-13C6] glucose was used to enhance the experimental sensitivity in vivo in the mouse brain and the 13C turnover curves of glutamate C4, glutamine C4, glutamate+glutamine C3, aspartate C2, lactate C3, alanine C3, γ-aminobutyric acid C2, C3 and C4 were obtained. A one-compartment model was used to fit 13C turnover curves and resulted in values of metabolic fluxes including the tricarboxylic acid (TCA) cycle flux VTCA (1.05 ± 0.04 μmol/g per minute), the exchange flux between 2-oxoglutarate and glutamate Vx (0.48 ± 0.02 μmol/g per minute), the glutamate-glutamine exchange rate Vgln (0.20 ± 0.02 μmol/g per minute), the pyruvate dilution factor Kdil (0.82 ± 0.01), and the ratio for the lactate conversion rate and the alanine conversion rate VLac/ VAla (10 ± 2). This study opens the prospect of studying transgenic mouse models of brain pathologies.