Measurement of 13 C turnover into glutamate and glutamine pools in brain tumor patients.

ABSTRACT

Malignant brain tumors are known to utilize acetate as an alternate carbon source in the citric acid cycle for their bioenergetics. 13 C NMR-based isotopomer analysis has been used to measure turnover of 13 C-acetate carbons into glutamate and glutamine pools in tumors. Plasma from the patients infused with [1,2-13 C]acetate further revealed the presence of 13 C isotopomers of glutamine, glucose, and lactate in the circulation that were generated due to metabolism of [1,2-13 C]acetate by peripheral organs. In the tumor cells, [4-13 C] and [3,4-13 C]glutamate and glutamine isotopomers were generated from blood-borne 13 C-labeled glucose and lactate which were formed due to [1,2-13 C[acetate metabolism of peripheral tissues. [4,5-13 C] and [3,4,5-13 C]glutamate and glutamine isotopomers were produced from [1,2-13 C]acetyl-CoA that was derived from direct oxidation of [1,2-13 C] acetate in the tumor. Major portion of C4 13 C fractional enrichment of glutamate (93.3 ± 0.02%) and glutamine (90.9 ± 0.03%) were derived from [1,2-13 C]acetate-derived acetyl-CoA.