The ratio of acetate-to-glucose oxidation in astrocytes from a single 13C NMR spectrum of cerebral cortex

J Neurochem. 2015 Jan;132(1):99-109. doi: 10.1111/jnc.12948. Epub 2014 Oct 14.

Abstract

The (13) C-labeling patterns in glutamate and glutamine from brain tissue are quite different after infusion of a mixture of (13) C-enriched glucose and acetate. Two processes contribute to this observation, oxidation of acetate by astrocytes but not neurons, and preferential incorporation of α-ketoglutarate into glutamate in neurons, and incorporation of α-ketoglutarate into glutamine in astrocytes. The acetate:glucose ratio, introduced previously for analysis of a single (13) C NMR spectrum, provides a useful index of acetate and glucose oxidation in the brain tissue. However, quantitation of relative substrate oxidation at the cell compartment level has not been reported. A simple mathematical method is presented to quantify the ratio of acetate-to-glucose oxidation in astrocytes, based on the standard assumption that neurons do not oxidize acetate. Mice were infused with [1,2-(13) C]acetate and [1,6-(13) C]glucose, and proton decoupled (13) C NMR spectra of cortex extracts were acquired. A fit of those spectra to the model indicated that (13) C-labeled acetate and glucose contributed approximately equally to acetyl-CoA (0.96) in astrocytes. As this method relies on a single (13) C NMR spectrum, it can be readily applied to multiple physiologic and pathologic conditions. Differences in (13) C labeling of brain glutamate and glutamine have been attributed to metabolic compartmentation. The acetate:glucose ratio, introduced for description of a (13) C NMR (nuclear magnetic resonance) spectrum, is an index of glucose and acetate oxidation in brain tissue. A simple mathematical method is presented to quantify the ratio of acetate-to-glucose oxidation in astrocytes from a single NMR spectrum. As kinetic analysis is not required, the method is readily applicable to analysis of tissue extracts. α-KG = alpha-ketoglutarate; CAC = citric acid cycle; GLN = glutamine; GLU = glutamate.

Keywords: acetate; glia; glucose; neuron.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Acetates / metabolism*
  • Acetyl Coenzyme A / metabolism
  • Animals
  • Astrocytes / chemistry
  • Astrocytes / metabolism*
  • Cerebral Cortex / chemistry
  • Cerebral Cortex / cytology
  • Cerebral Cortex / metabolism*
  • Female
  • Glucose / metabolism*
  • Glutamic Acid / metabolism
  • Glutamine / metabolism
  • Ketoglutaric Acids / metabolism
  • Magnetic Resonance Spectroscopy
  • Mice
  • Mice, Inbred C57BL
  • Neurons / chemistry
  • Neurons / metabolism
  • Oxidation-Reduction

Substances

  • Acetates
  • Ketoglutaric Acids
  • Glutamine
  • Glutamic Acid
  • Acetyl Coenzyme A
  • Glucose