Mitochondrial Krebs cycle keto acid pool depends upon input from pyruvate and glutamate to maintain homeostasis. We studied the affect of glucose-derived pyruvate removal on compensatory input from glutamine-derived glutamate by accelerated glutamate metabolism via glutamate dehydrogenase (GDH). In glutamine minus glucose media (Gln-Glc), NH(4)(+) production increased 41% without an increase in glutamine uptake consistent with accelerated glutamate metabolism via GDH. Alanine production dropped 40% consistent with a shift of glutamate from alanine aminotransferase (ALT) to GDH. Troglitazone (TRO) added to the Gln-Glc media further enhanced glutamate metabolism via GDH at the expense of glutamate metabolism via ALT since alanine production dropped an additional 70%. TRO reduced cell glutamate content 30% while increasing lactate production 5-fold consistent with blocking of cytosolic pyruvate formed from mitochondrial malate from reentering the cycle and maintaining keto acid pool homeostasis. Consequently mitochondrial keto acid pool deficit pulls glutamate via GDH into the cycle. Additionally TRO reduced cytosolic pH which effectively pushes glutamate via GDH, rather than merely shifting glutamate from ALT to GDH. Providing intramitochondrial pyruvate in the form of methyl pyruvate reduced glutamate metabolism via GDH and elevated glutamate metabolism via ALT to control levels restoring acid-base balance. Our findings are consistent with TRO regulation of anaplerosis dependent upon dual pull (cycle keto-acid deficit)/push (cytosolic acidosis) mechanisms.
Copyright © 2010 S. Karger AG, Basel.