Jean-Pierre Trezzi, Xiangyi Dong, Alexander Skupin, Jochen Schneider, Karsten Hiller
University of Luxembourg
Here, we present time-resolved dynamics of glucose metabolism in blood after oral administration of 13C stable-isotope labeled glucose in human subjects. To extract absolute flux values for glucose production (GP), glucose disappearance (GD) and gluconeogenesis (GNG)on a whole organism scale in diabetes patients, we developed a simple mathematical ODE based dynamic model that considers the main fluxes of (13C labeled) glucose into and out of the blood. In combination with the time-resolved enrichment patterns (Mass Isotopomer Distributions / MIDS) and absolute concentrations of the target metabolites obtained from DBS sampling and GC/MS measurement, we could determine quantitative and robust values for GP and GNG for each studied subject.
In mammals, the Cori cycle is a metabolic pathway that recycles alanine or lactic acid back to glucose: Lactic acid or alanine produced in metabolically active tissues is transferred into the blood stream and transported to the liver. The liver takes lactic acid and alanine up and recycles two of these molecules back to glucose in an energy consuming fashion (gluconeogenesis). The so assembled glucose is secreted back into the blood stream. Hepatic gluconeogenesis is essential for plasma glucose homeostasis and when dysregulated can be a cause for hyperglycemia, especially in type 2 in diabetes mellitus. The current diagnostic portfolio is solely aimed at determining the static fasting glucose level or the glucose excursion after an oral glucose load.
Using the available portfolio of diagnostic tools it is not possible to further characterize the underlying metabolic problem, and hence to apply an individualized therapy regime. An easy and directly applicable diagnostic tool to profile gluconeogenic fluxes as well as glucose clearance rates under resting conditions is still lacking.
Dried blood spots (DBS) have emerged as an easy sampling tool for human blood. On the other hand, stable-isotope labeling is a safe procedure to profile the dynamics of metabolite turnover on a whole organism scale. Here, we present time-resolved dynamics of glucose metabolism in blood after oral administration of 13C stable-isotope labeled glucose in human subjects. We developed a protocol to extract polar metabolites from dried blood spots and apply GC/MS to acquire MS data. To extract pure mass spectra from this complex data, we apply the ion-chromatographic deconvolution algorithm of our MetaboliteDetector software. Finally, based on the deconvoluted mass-spectra, we correct the data for naturally occurring stable-isotopes and determine mass isotopomer distributions (MIDs) for target metabolites. These time-resolved enrichment patterns (Mass Isotopomer Distributions / MIDS) in combination with absolute concentrations of the target metabolites both obtained from DBS sampling and GC/MS measurement are used as input for a simple mathematical ODE model. By solving the equation system of this model, we could determine quantitative and robust values for glucose production (GP) and gluconeogenesis (GNG) for each studied subject.
Due to the simple setup of our method (oral administration of the tracer and DBS sampling), such a sampling can even be performed by the patients themselves in home settings.