Measurement of ¹³C 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. 13C NMR based isotopomer analysis has been used to measure turnover of 13C-acetate carbons into glutamate and glutamine pools in tumors. Plasma from the patients infused with [1,2-13C]acetate further revealed the presence of 13C isotopomers of glutamine, glucose and lactate in the circulation that were generated due to metabolism of [1,2-13C]acetate by peripheral organs. In the tumor cells, [4-13C] and [3,4-13C] glutamate and glutamine isotopomers were generated from blood-borne 13C labeled glucose and lactate which were formed due to [1,2-13C[acetate metabolism of peripheral tissues. [4,5-13C] and [3,4,5-13C] glutamate and glutamine isotopomers were produced from [1,2-13C]acetyl-CoA that were derived from direct oxidation of [1,2-13C]acetate in the tumor.

The Leloir Cycle in Glioblastoma: Galactose Scavenging and Metabolic Remodeling

“…13 C NMR isotopomer analyses were performed as reported in our earlier publications [ 6 , 7 , 36 ]. Briefly, [U- 13 C]Glc is converted to [U- 13 C]pyruvate, via glycolysis, which in turn is converted to [U- 13 C]lactate by lactate dehydrogenase and [U- 13 C]alanine ( Figure 4 D showing lactate C3 signal (Lac3) at 20.80 ppm and alanine C3 signal (Ala3) at 16.88 ppm.…”

“…In the first turn of the TCA cycle, [1,2- 13 C]acetyl-CoA combines with unlabeled oxaloacetate and forms [4,5- 13 C]α-ketoglutarate/glutamate ( Figure 4 D showing Glutamate C4 signal (Glu4) at 34.20 ppm). 13 C-labeled lactate (Lac3), and glutamate (Glut4) can be readily detected by 13 C NMR spectroscopy and were used for 13 C isotopomer analysis [ 6 , 7 , 36 ]. The normalized peak areas of the 13 C- 13 C doublet (D23) and singlet (S) of Lac3 were obtained from the ratio of the peak area of the corresponding multiplet component (D23 or S) to the total area of the Lac3 signal (the sum of the peak areas of D23 and S).…”

“…Many human cancers, including brain tumors, primarily metabolize glucose (Glc) to lactate for ATP production, a phenomenon known as the Warburg effect [ 2 , 3 , 4 ]. Recently it has become apparent that malignant brain tumors also catabolize a wide range of circulating nutrients, including fatty acids, ketone bodies, amino acids, and acetate [ 2 , 5 , 6 , 7 ]. Glut3 (SLC2A3) is the major transporter of Glc in GBM, with its elevated levels indicative of poor patient outcomes [ 8 , 9 , 10 , 11 , 12 ].…”

Highlighting Functional Mass Spectrometry Imaging Methods in Bioanalysis

“…Isotope labeling is a key component to studying metabolic and cellular dynamics, and as noted above, stable isotope labeling can safely be used in human studies. − The multiscale capability of fMSI technologies can provide measures of dynamic heterogeneity in single cell or cell aggregates in biopsy specimens that may enhance diagnostic information gleaned from a single sample. , In addition, increased metabolic flux, rather than changes in steady-state levels, can be indicative of tissue pathologies such as breast cancer . The fMSI technique is positioned to provide a map of flux heterogeneity in clinical specimens that can detect high-flux subpopulations of cells that would likely be missed with standard tissue homogenization approaches.…”

NMR Metabolomics Methods for Investigating Disease

“…By contrast, studies that involve direct infusion of isotope tracers to humans are rare to date, but this trend is changing gradually. 68,69 Recently, a first-in-human in vivo metabolism protocol was used to study two different types of brain tumors using NMR spectroscopy. 13 C -labeled 3-hydroxy butyrate was infused intravenously, and its oxidation in the tumor was quantitated based on blood and resected tissue using NMR.…”