Comparison of [3,4‐¹³C₂]glucose to [6,6‐²H₂]glucose as a tracer for glucose turnover by nuclear magnetic resonance

Abstract

A recently introduced tracer, [3,4-13 C 2 ]glucose, was compared to the widely used tracer, [6,6-2 H 2 ]glucose, for measurement of whole-body glucose turnover. The rate of glucose production (GP) was measured in rats after primed infusions of [3,4-13 C 2 ]glucose, [6,6-2 H 2 ]glucose, or both tracers simultaneously followed by a constant infusion of tracer(s) over 90 min. Blood glucose was purified and converted into monoacetone glucose for analysis by 13 Multiple tracer methods have been introduced to measure systemic glucose turnover in vivo. These methods share the same physiologic principles, but differ in technical details such as the site of isotope labeling, the use of stable or radioactive isotopes, and detection techniques. Stable isotopes are now preferred for practical and ethical reasons despite lower sensitivity compared to radiotracers. If glucose turnover is the sole purpose of an experiment, mass spectrometry is usually chosen because of high sensitivity, simplicity of data interpretation, and wide application (1,2). However, if multiple stable isotopes or labeling patterns are used in a single study to probe additional metabolic pathways, then NMR offers the benefit that multiple sites of 13 C or 2 H labeling in a glucose molecule are easily distinguished. This property offers an overwhelming advantage compared to mass spectrometry.There is increasing interest in simultaneous measurement of both glucose turnover and other metabolic fluxes in vivo. For example, administration of 2 H 2 O followed by measurement of deuterium enrichment in positions 2, 5, and 6 of glucose by mass spectrometry allowed Saadatian et al. to calculate the relative rates of glucose production (GP) from glycerol, glycogen, and the TCA cycle (3). After co-administration of 2 H 2 O (oral) plus [6,6-2 H 2 ]glucose by continuous i.v. infusion, plasma glucose becomes enriched in multiple sites. The ratio of enrichment in position 5 compared to position 2 (or plasma water) yielded the fraction of plasma glucose derived from gluconeogenesis; whole-body turnover of glucose was measured from the 2 H enrichment at position 6. However, if detected by mass spectrometry, even [6,6-2 H 2 ]glucose is not an adequate tracer if other pathways are probed simultaneously by 2 H 2 O and by 13 C-enriched tracers (since m ϩ 2 could be due to additional neutrons from either 2 H or 13 C enrichment or both).A recently introduced tracer, [3,4-13 C 2 ]glucose, has multiple advantages compared to other 2 H-or 13 C-labeled glucoses (4). Unlike glucose enriched with a hydrogen tracer in position 2, the 13 C labeling is not influenced by cycling between glucose-6-phosphate and fructose-6-phosphate. This tracer also offers major advantages when detected by NMR. Glucose itself is an unfavorable molecule for NMR detection because of poor chemical shift dispersion and the presence of anomers, which effectively reduce signal and further complicate the spectra. A simple derivative, monoacetone glucose (1,2-diisopropylidene glucofuranose, also termed MAG), of...

The effect of short-term fasting on liver and skeletal muscle lipid, glucose, and energy metabolism in healthy women and men

“…Results were similar when the single apparent outlier among the women was excluded from the analysis. * P < 0.05; *** P < 0.001. by guest, on May 12, 2018 www.jlr.org Downloaded from glycogenolysis ( P < 0.001) ( Fig. 3A and 3B).…”

“…Assumptions regarding this model have been previously reported ( 21 ). Endogenous glucose production was measured by dilution of [3, [4][5][6][7][8][9][10][11][12][13] C]glucose as previously described ( 22 ). Fractional glycogenolysis and gluconeogenesis measured by 2 H-NMR was normalized with pyruvate carboxylase (PC)/phosphoenolpyruvate carboxykinase (PEPCK), pyruvate cycling and gluconeogenesis relative to TCA cycle fl ux measured by 13 C-NMR and the rate of endogenous glucose production (µmol/kg/min) was used to calculate the absolute fl uxes through each of these pathways ( 23 ).…”

“…Some individuals (women = 6, men = 5) were re-fed a low-fat meal (60% carbohydrate, 25% fat, and 15% protein; women = 567 and men = 667 kcal), and insulin and glucose excursion were assessed. In the 4 h after refeeding, peak insulin was signifi cantly higher in women (46 [37][38][39][40][41][42][43][44][45][46][47] vs. 20 [15][16][17][18][19][20][21][22][23][24][25] U/ml; P = 0.011), whereas peak glucose concentration did not differ between sexes ( P = 0.233). These fi ndings indicated reduced insulin sensitivity in women after short-term fasting.…”

Elevated TCA cycle function in the pathology of diet-induced hepatic insulin resistance and fatty liver

“…Steady state infusion of [3,[4][5][6][7][8][9][10][11][12][13] C 2 ]glucose was used to determine endogenous glucose production (EGP) using the tracer dilution approach (40)(41)(42). Briefl y, [3,[4][5][6][7][8][9][10][11][12][13] C 2 ]glucose was detected as the C3 D34 signal and the C4 D43 signal.…”

Role of Excess Glycogenolysis in Fasting Hyperglycemia Among Pre-Diabetic and Diabetic Zucker (fa/fa) Rats

“…Excess 2 H enrichment measurement in glucose. 2 H enrichment of the H2 position of glucose was measured using N,N-dimethylformamide-d 7 as an internal reference, as described previously (18). Also the natural abundance of methyl groups of MAG ( Fig.…”