Estimation of glucose carbon recycling and glucose turnover with [U-13C] glucose

Abstract

To estimate "true" rate of glucose production, as well as glucose carbon recycling in humans, a mass spectrometric method with [U-13C]glucose as tracer was developed. Because the opportunity for the uniformly labeled glucose, [13C6]glucose, to recycle back as [13C6]glucose is negligible, the true glucose production rate was obtained by measuring the plasma isotope enrichment of [13C6]glucose with chemical ionization mass spectrometry. In contrast, when the isotopic enrichment of C-1 of glucose was measured by enzymatic decarboxylation and ratio mass spectrometry, the "apparent" glucose production including carbon recycling was obtained. The difference between the two rates was the extent of glucose carbon recycling. [U-13C]glucose was administered as primed constant-rate infusion to six normal healthy adult subjects. Rates of glucose turnover were calculated from tracer dilution by applying steady-state kinetics. The true rate of glucose production estimated by the present method was 2.02 +/- 0.19 mg X kg-1 X min-1 (mean +/- SD). After an overnight fast, glucose carbon recycling contributed from 3 to 26% of the total glucose production rate. Use of stable isotopes and mass spectrometric technique permits estimation of important parameters of glucose metabolism without resorting to multiple tracers and at the same time preventing the risk of radiation.

Carbohydrate as nutrient in the infant and child: range of acceptable intake

“…Estimates of the rate of appearance of glucose (Ra) can be in¯uenced by the tracer isotope used (Kalhan, 1996) and by the particular population studied. The data displayed in Table 1 1982;Cowett et al, 1983;Sunehag et al, 1993;Kalhan, 1994;Arslanian & Kalhan, 1992, 1994Austin et al, 1994;Amiel et al, 1991;Tserng & Kalhan, 1983). The rates of glucose turnover in the preterm infants are approximated from published reports because of the scarcity of true basal data in this population.…”

“…The endogenous rate of production of glucose expressed per kg body weight is highest in the immediate neonatal period and gradually decreases with age. During puberty the rate of production of glucose is signi®cantly higher than that in adults (Arslanian & Kalhan, 1992, 1994Austin et al, 1994;Amiel et al, 1991;Tserng & Kalhan, 1983). Based on respiratory exchange data, it can be inferred that 65 ± 75% of glucose produced (Ra) is oxidized to carbon dioxide.…”

Sensitive LC MS quantitative analysis of carbohydrates by Cs+ attachment

“…Sample preparation for large sample lots, which frequently occurs in clinical studies, is an important rate-limiting step for sample throughput, and thus, is both costly and labor intensive. For example, glucose analysis by GC/MS from the aldonitrile pentaacetate derivative requires five different chemical steps including protein precipitation, deionization, two steps of derivatization, and extraction before analysis [15]. Inexpensive derivatization reagents however, such as acetic anhydride, do not provide optimum volatility for carbohydrates, reducing sensitivity, limiting analysis to abundant species such as glucose.…”

Reducing dietary fat from a meal increases the bioavailability of exogenous carbohydrate without altering plasma glucose concentration

“…The tracer-to-tracee ratio (TTR) of plasma glucose ( 13 C: 12 C ratio) was measured by electron impact ionization gas chromatography-mass spectrometry (Agilent 5973Net-works, Mass Selective Detector; Agilent Technologies, Palo Alto, CA) after conversion to the aldonitrile derivative of glucose in deproteinized plasma (39).…”