Astroglial contribution to brain energy metabolism in humans revealed by 13C nuclear magnetic resonance spectroscopy: elucidation of the dominant pathway for neurotransmitter glutamate repletion and measurement of astrocytic oxidative metabolism.
Increasing evidence supports a crucial role for glial metabolism in maintaining proper synaptic function and in the etiology of neurological disease. However, the study of glial metabolism in humans has been hampered by the lack of noninvasive methods. To specifically measure the contribution of astroglia to brain energy metabolism in humans, we used a novel noninvasive nuclear magnetic resonance spectroscopic approach. We measured carbon 13 incorporation into brain glutamate and glutamine in eight volunteers during an intravenous infusion of [2-13C] acetate, which has been shown in animal models to be metabolized specifically in astroglia. Mathematical modeling of the three established pathways for neurotransmitter glutamate repletion indicates that the glutamate/glutamine neurotransmitter cycle between astroglia and neurons (0.32 +/- 0.07 micromol x gm(-1) x min(-1)) is the major pathway for neuronal glutamate repletion and that the astroglial TCA cycle flux (0.14 +/- 0.06 micromol x gm(-1) x min(-1)) accounts for approximately 14% of brain oxygen consumption. Up to 30% of the glutamine transferred to the neurons by the cycle may derive from replacement of oxidized glutamate by anaplerosis. The further application of this approach could potentially enlighten the role of astroglia in supporting brain glutamatergic activity and in neurological and psychiatric disease.
Lebon
Vincent
V
Howard Hughes Medical Institute, Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
Petersen
Kitt F
KF
Cline
Gary W
GW
Shen
Jun
J
Mason
Graeme F
GF
Dufour
Sylvie
S
Behar
Kevin L
KL
Shulman
Gerald I
GI
Rothman
Douglas L
DL
D000085:Acetates / Q000008:administration & dosage / Q000378:metabolism; D000328:Adult; D001253:Astrocytes / Q000378:metabolism*; D001921:Brain / Q000378:metabolism*; D002247:Carbon Isotopes; D002952:Citric Acid Cycle; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism*; D005973:Glutamine / Q000378:metabolism; D006801:Humans; D007262:Infusions, Intravenous; D007656:Ketoglutaric Acids / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008959:Models, Neurological; D009413:Nerve Fibers, Myelinated / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D010084:Oxidation-Reduction; D010101:Oxygen Consumption / Q000502:physiology
D000085:Acetates; D002247:Carbon Isotopes; D007656:Ketoglutaric Acids; D005973:Glutamine; D018698:Glutamic Acid