Localized 13C NMR spectroscopy in the human brain of amino acid labeling from D-[1-13C]glucose

Cerebral metabolism of D[1-13C]glucose was studied with localized 13C NMR spectroscopy during intravenous infusion of enriched [1-13C]glucose in four healthy subjects. The use of three-dimensional localization resulted in the complete elimination of triacylglycerol resonance that originated in scalp and subcutaneous fat. The sensitivity and resolution were sufficient to allow 4 min of time-resolved observation of label incorporation into the C3 and C4 resonances of glutamate and C4 of glutamine, as well as C3 of aspartate with lower time resolution. [4-13C]Glutamate labeled rapidly reaching close to maximum labeling at 60 min. The label flow into [3- 13C]glutamate clearly lagged behind that of [4-13C]glutamate and peaked at t = 110-140 min. Multiplets due to homonuclear 13C-13C coupling between the C3 and C4 peaks of the glutamate molecule were observed in vivo. Isotopomer analysis of spectra acquired between 120 and 180 min yielded a 13C isotopic fraction at C4 glutamate of 27 ± 2% (n = 4), which was slightly less than one-half the enrichment of the C1 position of plasma glucose (63 ± 1%), p < 0.05. By comparison with an external standard the total amount of [4-13C]glutamate was directly quantified to be 2.4 ± 0.1 μmol/ml-brain. Together with the isotopomer data this gave a calculated brain glutamate concentration of 9.1 ± 0.7 μmol/ml, which agrees with previous estimates of total brain glutamate concentrations. The agreement suggests that essentially all of the brain glutamate is derived from glucose in healthy human brain.

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Journal of Neurochemistry, 63, 4, 1377-1385

 Record created 2012-05-26, last modified 2018-03-17

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