Effects of ketone bodies on astrocyte amino acid metabolism.
The effects of acetoacetate and 3-hydroxybutyrate on glial amino acid metabolism were studied in primary cultures of astrocytes. The exchange of nitrogen among amino acids was measured with 15N as a metabolic probe and gas chromatography-mass spectrometry as a tool with which to quantify isotope abundance. Addition of either acetoacetate or 3-hydroxybutyrate (5 mM) to the incubation medium did not alter the initial rate of appearance of [15N]glutamate in the glia, but it did inhibit transamination of glutamate to [15N]aspartate. Addition of acetoacetate also inhibited formation of [2-(15)N]glutamine, but 3-hydroxybutyrate had a stimulatory effect. The presence in the medium of sodium acetate (5 mM) was also associated with diminished production of [15N]aspartate and [2-(15)N]glutamine with [15N]glutamate as precursor. Studies with [2-(15)N]glutamine as precursor indicated that treatment of the astrocytes with ketone bodies did not alter flux through the glutaminase pathway. Nor did the presence of the ketone bodies reduce significantly the flux of nitrogen from [15N]GABA to [2-(15)N]glutamine when the former species served as a metabolic tracer. The concentration of internal citrate increased in the presence of acetoacetate, 3-hydroxybutyrate, and acetate. Studies with purified sheep brain glutamine synthetase showed that citrate inhibited this enzyme. These findings are considered in terms of the known anticonvulsant effect of a ketogenic diet.
Yudkoff
M
M
Division of Child Development, University of Pennsylvania School of Medicine, Children's Seashore House and Children's Hospital of Philadelphia 19104-4318, USA.
Daikhin
Y
Y
Nissim
I
I
Grunstein
R
R
Nissim
I
I
D020155:3-Hydroxybutyric Acid; D000090:Acetoacetates / Q000494:pharmacology; D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism; D001253:Astrocytes / Q000187:drug effects* / Q000378:metabolism*; D002478:Cells, Cultured; D019343:Citric Acid / Q000494:pharmacology; D008401:Gas Chromatography-Mass Spectrometry; D005974:Glutamate-Ammonia Ligase / Q000037:antagonists & inhibitors; D018698:Glutamic Acid / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D006885:Hydroxybutyrates / Q000494:pharmacology; D007657:Ketone Bodies / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012756:Sheep; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D000090:Acetoacetates; D000596:Amino Acids; D006885:Hydroxybutyrates; D007657:Ketone Bodies; D005973:Glutamine; D019343:Citric Acid; D001224:Aspartic Acid; D018698:Glutamic Acid; C016635:acetoacetic acid; D005680:gamma-Aminobutyric Acid; D005974:Glutamate-Ammonia Ligase; D020155:3-Hydroxybutyric Acid