1. Department of Neurology and Neurotherapeutics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, USA;2. Department of Pediatrics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, USA;3. Department of Mathematical Sciences, University of Texas at Dallas, Richardson, Texas, USA;4. Advanced Imaging Research Center, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, USA;5. Department of Radiology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, USA;6. Department of Chemistry, University of Texas at Dallas, Richardson, Texas, USA;7. Department of Internal Medicine, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, USA;8. VA North Texas Health Care System, Dallas, Texas, USA
Abstract:
The 13C‐labeling patterns in glutamate and glutamine from brain tissue are quite different after infusion of a mixture of 13C‐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 13C 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 1,2‐13C]acetate and 1,6‐13C]glucose, and proton decoupled 13C NMR spectra of cortex extracts were acquired. A fit of those spectra to the model indicated that 13C‐labeled acetate and glucose contributed approximately equally to acetyl‐CoA (0.96) in astrocytes. As this method relies on a single 13C NMR spectrum, it can be readily applied to multiple physiologic and pathologic conditions.
