Refined Analysis of Brain Energy Metabolism Using In Vivo Dynamic Enrichment of 13C Multiplets

Carbon-13 nuclear magnetic resonance spectroscopy in combination with the infusion of C-13-labeled precursors is a unique approach to study in vivo brain energy metabolism. Incorporating the maximum information available from in vivo localized C-13 spectra is of importance to get broader knowledge on cerebral metabolic pathways. Metabolic rates can be quantitatively determined from the rate of C-13 incorporation into amino acid neurotransmitters such as glutamate and glutamine using suitable mathematical models. The time course of multiplets arising from C-13-C-13 coupling between adjacent carbon atoms was expected to provide additional information for metabolic modeling leading to potential improvements in the estimation of metabolic parameters. The aim of the present study was to extend two-compartment neuronal/glial modeling to include dynamics of C-13 isotopomers available from fine structure multiplets in C-13 spectra of glutamate and glutamine measured in vivo in rats brain at 14.1 T, termed bonded cumomer approach. Incorporating the labeling time courses of C-13 multiplets of glutamate and glutamine resulted in elevated precision of the estimated fluxes in rat brain as well as reduced correlations between them.