Measurement of glucose metabolism in the occipital lobe and frontal cortex after oral administration of [1-13C]glucose at 9.4 T

Abstract

For the first time, labeling effects after oral intake of [1-13C]glucose are observed in the human brain with pure 1H detection at 9.4 T. Spectral time series were acquired using a short-TE 1H MRS MC-semiLASER (Metabolite Cycling semi Localization by Adiabatic SElective Refocusing) sequence in two voxels of 5.4 mL in the frontal cortex and the occipital lobe. High-quality time-courses of [4-13C]glutamate, [4-13C]glutamine, [3-13C]glutamate + glutamine, [2-13C] glutamate+glutamine and [3-13C]aspartate for individual volunteers and additionally, group-averaged time-courses of labeled and non-labeled brain glucose could be obtained. Using a one-compartment model, mean metabolic rates were calculated for each voxel position: The mean rate of the TCA-cycle (Vtca) value was determined to be 1.36 and 0.93 μmol min−1 g−1, the mean rate of glutamine synthesis (Vgln) was calculated to be 0.23 and 0.45 μmol min−1 g−1, the mean exchange rate between cytosolic amino acids and mitochondrial Krebs cycle intermediates (Vx) rate was found to be 0.57 and 1.21 μmol min−1 g−1 for the occipital lobe and the frontal cortex, respectively. These values were in agreement with previously reported data. Altogether, it can be shown that this most simple technique combining oral administration of [1-13C]Glc with pure 1H MRS acquisition is suitable to measure metabolic rates.

Mapping of Glutamate Metabolism using 1H FID-MRSI after oral Administration of [1-13C]Glc at 9.4 T

“…Figure 2c illustrates that these spectral pattern changes arise from 13 C labeling of Glu, Gln, Asp and the increase of the sum of 12 C and 13 C labelled Glc concentration. These changes are consistent to results shown in in 1H SVS data at 9.4T after oral Glc administration 24 .…”

“…The PE of Glu4 from the present study is slightly higher than the values after 2 to 3h (when saturation is expected) from other oral studies administering the same amount of [1- 13 C]Glc (20-24% 24,49 ) or less [1-13 C]Glc (16% using 0.65 g Glc/kg body weight instead of 0.75 g/kg 50 ). Most studies use i.v.…”

“…studies (10-25% 49,52,53 ). The herein presented Glx3 values are at the upper range of previous values for oral administration (17-19 % after 2h 24 ) or i.v. protocols (5-10% 23 and 23% 53,54 ).…”

“…The temporal changes of the spectra give insights into the speed of the corresponding metabolic processes. So far, Boumezbeur's method was applied in only a few studies in animal brain 20,21 and recently also in human brain 7,[22][23][24] . These studies measured the temporal changes in the MR spectra in a maximum of two voxels.…”

“…So far, Boumezbeur’s method was applied in only a few studies in animal brain 20,21 and recently also in human brain 7,22–24 . These studies measured the temporal changes in the MR spectra in a maximum of two voxels.…”